First and foremost, because it doesn't work. At best, you will just embarrass yourself.
It is, usually, a guy who learns and uses methods to manipulate female psyche to achieve his goals (usually sex with said female).
Exactly what others have said. The "manipulation" part. It's creepy. Yes, I know how PUAs feel about the word "creep" and that's exactly why I chose it, because I think it needs to be said. You don't "manipulate" someone into sex, and if it actually does somehow work then the only reason it did is because she considered you interesting or attractive enough to see past the creepiness or (more likely) she's trashy . If you're trying to "manipulate" someone into sex it shows a clear lack of respect.
blackrave said:
What is make-up, fake nails/hair/eyelashes, push-up bras, shape improving lingerie, high heels, revealing clothes, etc., if NOT manipulation of male psyche.
Heaven forbid someone want to look nice because they enjoy looking nice and not for sex. No one has ever said men can't do the same thing, ie, improve their appearance to make themselves more sexually appealing (or, you know, because you want to look better for its own sake). Putting on make-up (for women) or going to the gym (for men) is a pretty far cry from fondling someone in order to break down her "token resistance".
But let's go a bit deeper into your reference to "the male psyche". Reason 2 I dislike PUAs is the idea that my weak male brain responds only to sexual urges. At its core, it's misandrist.
And feminine flirting methods aren't something people shun or hate.
PUAs aren't flirting, and there are no "flirting methods". Flirting is just something you do when you have some fun talking to someone of the opposite sex, not an active and calculated effort to manipulate someone into doing your bidding.
Other reasons:
Evolutionary psychology of the sort PUAs use is just bullshit. While evolutionary psychology is important in psychological research, it's for questions like "Why are some people genetically predisposed to have arachnophobia", not for saying things like "Women are worse at math because men did the hunting" or "Women don't like/need sex because men are the ones that need to spread their seed." There is no validity to these claims, they are pseudoscience of the most ridiculous kind.
Actually, I'm just going to generalize that to most if not all of it being bullshit. It doesn't work, and will never work.
It turns sex into a target or goal and puts it on a pedestal as something you need to be actively working towards, which is setting you up for massive disappointment. Sex isn't a goal, it's something that just happens between two people, sometimes when you're not even done with middle school and sometimes not until you're well into your 20s or even later. The more effort you spend trying to get it, the more you'll just end up beating yourself up for not having it yet and the more disappointed you'll be when you do start having sex and realize it's not the massively huge deal you worked it up to be in your mind.
The adversarial outlook on sex is just not a healthy way to be going through life.
Finally, some PUA authors have been known to target individuals with autism spectrum disorders when what such people really need is therapeutic intervention, which is just low. They're playing on how seriously depressed some people with ASDs become over their difficulties with having social lives, they're setting them up for further disappointment when these "techniques" inevitably fail. Also, because taken as literally as some people with ASDs take things many of these "techniques" are basically indistinguishable from sexual assault, it puts young people on the spectrum at risk of serious disciplinary penalties when their "target" decides to report the PUA's increasingly aggressive and insistent attempts to get into her pants, which will make learning how to function socially even more difficult.
