I believe they ended up messed up psychologically because PUA is not based on being honest or authentic. Instead, it's based on developing a fake persona, using fake routines, techniques, tactics, etc and essentially lying to women. They're hiding their true selves and their true romantic/sexual intent with women instead of being authentic and direct with women.
This eventually eats away at their soul, manifesting itself as some form of psychological problems.
The 2nd reason they end up messed up is because they don't have any purpose in life beyond 'PUA, which ultimately is not a deeply fulfilling existence. They base their 'happiness' on how well they're doing with women, which is not healthy for their state of mind.
I believe at the core we all yearn to be our authentic self and to have a purpose in life beyond merely picking up women.
This is one reason I left the whole indirect PUA stuff alone years ago. It was fun for a while, but ultimately left me feeling empty, fake and unfulfilled. I decided to switch to an honest, direct and authentic way of approaching and interact with women as well as focus on goals which make me fell fulfilled in life.
This is what why I believe Neil Strauss eventually denounced PUA and his fake persona 'Style'. He wanted to be more authentic and life a more fulfilling life than the path of being a PUA.
It's also the reason the 'PUA community itself is essentially dead. Ultimately it could not last forever because it was not built on a foundation of honestly or authenticity. Eventually the guys who got into PUA realised this and yearned for a deeper existence beyond being a PUA.