Sometimes I think that they make it harder to just be nice or that they 'ruin' girls for other guys, but to be honest I'm still not convinced that just being nice would work. Women will be friends with you if you're sweet and might sleep with you if they're in the mood, but for actual long-term relationships they're pretty demanding and you really have to bring a lot to the table... and to be honest, it's not very often where I meet someone and feel like it's worth the effort, or like I could even begin to fulfill her expectations once I stop putting so much effort into impressing her/trying to be what she wants me to be.
I'm not going to defend these PUA people, but I do understand where they're coming from-- a lot of them aren't so different from me. They're mostly just normal guys who are sick of being rejected after trying things the 'normal way', so they try to score by being douchebags.
They're the same guys who probably would have been able to do pretty well for themselves in the 50s, back when women couldn't actually support themselves, but now find themselves pushed aside and in many cases making less money than the women who still expect them to 'be the man'... so the way they see it, they're faced with a choice-- either do the PUA schtick and score a lot of empty encounters that alleviate your boredom and bolster your ego, or allow yourself to be rejected over and over and over until you die alone and full of regrets.