This is a painful thread. Hard for me to participate without powerleveling as it hits really close to home, but I'll share some loose thoughts.
First, I really disagree with immediate labelling of "nice guys" as rapists in the making and on the whole horrible people. It is true that many of them come off as passive-aggressive wankers, but oftentimes so do those who criticise them. Women excel at that. You almost get the impression that there's some physical disgust they experience and try to rationalise it - "how dare that creep even THINK about sleeping with me? he must be a rapist" etc.
Second, I think the problem of "nice guys" lies in their lack of experience with relationships. That has two consequences:
1. They think they can create a happy relationship just by being nice. Now, let's assume that a guy is genuinely nice (as in, good-natured, kind, friendly etc.) and not just thinking of himself as such. This alone, however, is not enough and it shows whenever a situation occurs that triggers their relationship-related insecurities. It can happen, for example, at a party when other guys approach the girl they are with. This is a test many "nice guys" fail. They fear losing the girl and start acting like overprotective, jealous assholes. Or, for example, they completely lose their shit and the "nice guy" facade when they're at a restaurant with the girl of their dreams and the service is taking too long.
2. They think that a relationship is necessary for them to become normal human beings, because everyone else seems to be in one and a happy one, too. They can hardly be blamed for that, because mass culture tells them every day that they need to sleep around a lot and be in a relationship with plenty of sex involved just to be considered a real human being. Since many "nice guys" also lack social skills and friends, they cannot confront those messages with how real world works and fall for them very easily. That way women who don't want to sleep with them become also some kind of existential enemies who prevent them from becoming part of humanity (think Mary Lee Walsh). The delusional embrace of the manosphere is just around the corner for them. This is indeed very sad irony that people who consider themselves "red-pilled" are almost entirely conditioned by pop-culture and mass-media, at least as far as relationships are concerned.
My advice to "nice guys" would be, well, to forget about relationships completely, take up a martial art (raises assertiveness, confidence AND makes you look better) and develop social skills, helping yourself with booze if necessary. As your socialisation progresses, you'll realise that many people around are in fact poseurs and walking sacks of insecurities themselves, that many happy couples actually hate each other and many times that really hot girl is only with that other guy for his money, which means you could just as well buy her "affection" yourself. You'll also realise that many hot, princess-like girls are batshit insane with issues way worse than yours. And that it's much better to be alone than to be in a destructive relationship with a psycho "cutie".
Don't forget claiming to be against "degeneracy" (a.k.a. "I can't get laid because die Juden told white women to fuck niggers instead of me").