Well even if it has fascist origins (genetic fallacy, it doesn't matter where it came from, just if it's right), the fact is it can't predict anything specific beyond what chance would allow, and the rest is fuzzy enough to apply to everyone (you will encounter difficulty in the future, GEE there's a shock). The total lack of any scientific predictive power is another thing, and it's also logically self contradictory in any explanation they offer.
To expand on that, scientific predictive power. This concept was concieved early on, and astrology USED to include the body of knowledge about the locations of stars and such (this was the accurate info, and as such it was kept when astronomy divorced itself from whatever lacked evidence). However, the rest of the basic cosmology was flat out off. It was concieved in a time when the constallations were thought to actually be physical things of themselves, a link between stars, gods, something like that. Further, the stars were assumed to be MUCH closer, directly overhead, as they appeared to move every night (the earth was assumed fixed in the center of it all). Further, they were actually holes in the firmament, or massive dome made from holy glass of some sort holding up the sky. The planets (planet being a word that originally meant "wanderer") were thought to be far closer as well, and as they travelled in strange paths, sometimes appearing to go backwards for a moment before continuing (an illusion caused by the perception that earth is what they were encircling), and so they assumed predictive power. It is very important to note that they only saw a few of these wanderers, out to Saturn.
The question comes up. If there was any value in astrology, why has it made NO predictions regarding advancing science, and it was instead astronomy that made every single discovery we've made about the heavens, EVER? Not a single astrologer ever said "there is a slight discrepency in the accuracy of our predictions which suggests another wanderer, possibly in this location", mainly because they never CHECKED for accuracy, merely stating they were totally accurate (because to them, an admission of possibly being wrong in some details is seen as a weakness). Meanwhile, astronomers start peering deeper into space and finding new planets in the skies, and over time as understanding of how planets move improves (thanks to Newton), some scientists say that there is irregularity in the orbits of some of the planets that suggests a large gravitational body nearby, likely another planet, and that's how they discover one of them. This is long after they find out things like the lack of a glass dome, showing that their measurements of how the planets move suggests a Heliocentric model of the solar system, and just how far away all those things are. Also, they discover that the rules that govern the motion of bodies in the heavens are the same rules that govern how things happen on Earth (Galileo, and again, Newton). Meanwhile, Astrology pretends like it never said anything about domes or geocentric models and despite the total upheavel of their cosmology, they go on like nothing's changed and it's exactly as accurate as ever.
They never update, never change, still don't predict a single scientific discovery. Meanwhile, scientists find that the universe (aside from the wanderers, earth included) does not revolve around the sun, but the center of a massive cluster of stars they call the galaxy. Further, the location of our solar system in this mess is pretty far away, and over time as our system revolves around the center of this mass, the locations of constellations shift to the point where someone's star sign is now a full month shifted away from where it was when astrology was first formed.
The astrologers ignore this. Virgos aren't virgos, scorpios aren't scorpios, but they make the exact same predictions the same way (yes, taking into account much more accurate timing than just month) but without once accounting for this shift, at all. It's like the star's locations matter but... they don't matter enough to keep track of the constellations. But, it's really the planets eh? Well then why is it that they DID update that with new science? They claim the same accuracy, like nothing's changed, even though they never once considered Pluto or Neptune in the past before they were discovered, but now they do use them in calculations. Do the planets only control our lives if we know they are there? If I erased human knowledge of the locations of the planets, would we be free of fate, or die or something?
Now here's where it gets silly. Astronomy keeps updating itself, finding new info and correcting old ideas to match the new discoveries. Scientists seem to think being able to update your understanding of things with new discoveries is a STRENGTH of their system instead of a weakness. Insane right? As a result, they discover extrasolar planets, though they had predicted them long before due to having a basic understanding of planet formation. Of course, the nature of these extrasolar (outside the Sol system) planets is different than expected, so they revise their understanding of planet formation with each new discovery (and happily). How do the astrologers handle this? So far, they ignore it. They seemed fine adding Neptune, Uranus, and Pluto to the mix, but there's just so many extrasolar planets that I guess they decided it was too messy and to just ignore it. Maybe they are too far away? Maybe being in orbit of those stars they control the fates only of any aliens in those systems? Either explanation they use, they form cognitive dissonance that wrecks their little hypothesis.
Now first thing's first, there's no point trying to explain a phenomenon unless you can confirm there IS something to explain. It's silly to explain how a murder weapon got into someone's house if you haven't even found any evidence it's in someone's house after all. However, that sort of cart-before-the-horse science happens all the time with the antiscience groups. They like to assume their conclusion as the premise to show it's true all the time. With that in mind, astrologists attempting to "explain how astrology works" when they haven't even shown THAT it works is an excercise in crazy. Still, as even those explanations are bunk let's head to that.
First of all, there's nothing wrong in positing an "unseen unknown force". It happens in science all the time, as in the discovery of x-rays (in fact most forces are unseen). However, first you need evidence it's there, and that's gathered by eliminating all the known forces for a phenom. However, that force's attributes do have to be logically consistant if you are going to try to define it.
Now astrologers have posited a few known forces in the past. For example, for a while gravity was all the rage. When it was shown that gravity's behavior is well understood (though not the cause as of yet, it's a weird force in that sense), and that it's effects drop (with the square of the distance) the further one gets from the source, and further that it is not fine tuned from ANY of the planets and if it is strong enough to pull a chemical in one's brain, it'll pull ALL of it in the same direction and the makeup of a brain is more complicated than a processor and the "using a hammer on a hard disk to program windows" approach of it's control is basically insane, they dropped that. Then there was light, but that's right out for the same reasons.
So, they posited an unknown force as of yet undiscovered. Now again, since astrology has not even been confirmed to exist, positing this force is jumping the gun by a crazy amount, but here's the things that would have to be true. First of all, distance would have to not be a factor. That is, like a laser, it would not disperse and would remain just as strong no matter how far. This would need to be the case considering the sheer spaces between planets. If distance did matter, the moon would outweigh every single other object in the solar system by orders of magnitude. However, every planet has equal weight in their predictions, thus that is clearly not the case. Second of all, size of the object can't matter. This is because if size was a factor, the sun would outweigh everything else by orders of magnitude, and for those charts that don't use the sun, jupiter would still dominate by several times the size of the next contender, Saturn. As those have equal weights in astrology, size can't be an issue.
But wait! What about, other planet's moons, and asteroids, and planetoids, and comets, and every single spec of dust out there, and man-made satellites? If distance doesn't matter, and size doesn't matter, why don't they count? Well this brings up a fatal contradiction of course and I could end it here, but let's go on. It's worse than that. When Pluto was declared a planet, it got used in predictions. However, as we all know, Pluto isn't a planet any more. The dividing line between "planet" and "not planet" is fuzzy, because that's how the universe just happens to be. There's no clear point between it all and any definition is going to have certain objects with characteristics that make it qualify and yet seem "wrong" to our human brains as planets. The point of this is it messes up astrologers too, because they need something to be clearly a planet to use it in their calculations. Since the universe doesn't ablige them with clear deliniations, they are out of luck, but scientists aren't. They know the definitions of "planetness" are fuzzy, and they go with it, redefining as they go. Astrologers can't do that though, and they certainly couldn't admit that they were using Pluto all this time but shouldn't have (because they would either have to say "all our predictions since we started using Pluto have been off, but that's better now" (a public relations disaster) or "we're going to stop using Pluto now and also our predictions are just as accurate either way" (a logic disaster). So they have to basically keep using Pluto and say that the astronomers are wrong to say it's not a planet (though since Pluto is duel orbitting it's "moon" as more of a double planet system, why they don't use Charon now since they are no longer going with astronomer's defintions of planets as their own is anyone's guess). So again, they are logically defeated by a major contradiction in terms. They seem to go with only the objects that are actually CALLED planets, but now just go with their own definition. Whereas with the astronomers, it doesn't really matter if they call it a planet or not (just what the characteristics of the object are), in astrology it clearly does matter, so if they have contradictions in their new definitions, that's a problem. What aspect are they looking for to decide that Pluto is a planet but Charon (and other objects that are basically just like Pluto) aren't. Clearly it isn't if it's icey or gassy or rocky, because the things they count as mattering run all over that spectrum of spectrums.
Lastly, why aren't they counting the extrasolars? We've established that distance doesn't matter, and we've established that size doensn't matter, so why not? And, why not other stars, or other stranger objects? No matter how they want to define this force, it's a logical contradiction. When it comes down to it though, that's because these places are NOT affecting us!
There's the key right there. Every single properly controlled test ever done on astrology has shown it to be no greater than chance. They've even tested those extremely vague predictions just to see if they are more specific than they seem. That's an easy one. You get a number of people to test, and then mark a number of envelopes, 1-20. You know what's in each one, but the person who hands them out won't. That person picks them up after you've left the room with your list of what matches what number. That person then notes down which student s/he's passing out which envelope to, and so on. Well, actually in THIS case, recording who gets what and what's in each envelope is pointless (the control of the second person not knowing however is needed), and I'll explain why. Every single one has the same prediction. This one will be created by an astrologer FOR a specific person. That person is picked randomly and the astrologer won't get any information except what the astrologer says they need, and this will be limited to info that won't give away everything about that person (otherwise the astrologer already shows their lack of ability by establishing they need to know the person's past to give them info on their past). The astrologer, barring those bits of info that would invalidate the test outright, will be the one to define what info they need (anything else and you aren't testing that astrologer's claim). The astrologer will define what they can do, to what accuracy, and under what conditions. So long as the accuracy and conditions don't result in logically reducing their ability to exactly what we know can happen anyway (that is, if they say they can flip a coin up heads with an accuracy of 50%) and they don't define conditions that would invalidate the test outright (that is, saying they can find gold deposites underground so long as they can see a map of where gold deposites are located underground), then the test will go from there (so basically, there'd be no problem if say they needed to be in a room painted entirely blue or holding some special crystal (so long as it isn't a cell phone), barring extreme costs (not a logical prevention but in this case making the test impractical beyond reason, which sometimes is a tactic that makes one ask if the one making the claim of a power EVER achieves those conditions and if not, how they ever got the idea they have such a power).
So yeah, THIS particular test, whenever it's done, concludes with everyone reporting how accurate they say the test is. The trick that makes this one easier than some other tests is EVERY SINGLE astrology report is the exact same one that astrologer wrote for that one random person. That person is among them, and no one knows who the person is, including that one person. Really this sort of common testing would make for a great weekly reality show. I'd even endure the pulsing "drama music" as cameras zoom in for "reaction shots" and made up "trauma" for minutes on end. Every time this test is done, the gauging everyone does is, on average, a conclusion that yes this is very specific to me, and the one person it was actually for doesn't rank it any higher on average than the rest of them. Sometimes it's lower (but not by a statistically significant amount) and sometimes higher (ditto), but it's usually pretty much where you'd expect it if astrology was bunk.
So okay maybe it's not true. But, what harm does it do? Let me ask you something. Do you think assuming patently untrue things about the world and making decisions BASED on those assumptions is likely to get you results in line with what you expect? There are companies deciding when to launch products or what things to make based on astrology predictions. Very often, those who use this information for a large part of how they run things tend to lose a lot of money year after year until they fire the astrologer. Some of them aren't affected namely because they only give their opinions a "weight" and it only throws off whatever else they use by so much (some of it also nonsense anyway). Individual people deciding how to run their personal lives can screw things up too. A person seeking love being told it isn't in the stars for several months will maybe miss a lot of opportunities if they take that astrology reading seriously. Conversely, someone with a serious illness told that the stars say they will get better shortly who takes that advice seriously may ignore doctor checkups until it's too late. Doesn't look so innocent now does it? At the very least, if they don't get into any of those situations, they are spending time and money on something that doesn't do anything but that they expect will. Isn't that reason enough to consider it harmful?
After ALL that, am I honestly expected to humor peope when they bring it up? Is "being polite" really worth it? Is it really rational for me to spout something like "well maybe it's possible" when it is so very clear that everything I know says no, it really isn't? Isn't doing anything other than making it very clear exactly what I think of their delusion just fueling their fantasy? Don't we generally consider that sort of thing pretty harmful? So no, my reaction is either to just not say a single thing or just tell it like it is. I refuse to politely say something I know isn't true to further a belief that very likely would just hurt them down the line. If you've read everything I typed above, you can see why.