When a young woman has trouble with life she's given sympathy and resources. When a young man has trouble he's told to stop being such a wimp. Not surprisingly some of them snap.
The problem of discouraging men from expressing their emotions nonviolently is definitely not confined to these boards, however. I see tons of characters in media and people in real life who model the idea that anger or violence, while bad, are understandable ways for a man to express feelings (the same sentiment for women is much rarer). It might be bad that a man did something violent, but it doesn't undermine his very identity by eroding his masculinity in the same way that weeping and sobbing and being sensitive might.
I can't count the number of times I saw guys punching walls in movies growing up, often in circumstances where their characters were really feeling sad or hopeless or hurt. Women in movies under the same circumstances would often cry or be consoled. Or to put it another way, in a movie scene with a man and woman under extreme stress in a room together, I've never seen the woman punching holes in her own walls while the man sits on the bed crying. There are tons of other examples of stress reactions that are usually modeled in media along gender lines in this same way.
I think this stuff is self-fulfilling. Guys are discouraged from acknowledging difficult feelings except through stoicism or anger, and in turn people continue to associate that behavior with guys. When men on 8chan start buying into racist ideology and feeling like they can only express their distress through anger and violence, it seems inevitable that things like shootings will follow. The copycat effect with shootings that already happened only encourages it (see how this shooter cited the NZ shooter as inspiration).
I think things are improving, but I think that until guys are trained to express a full spectrum of emotions openly and without shame, and people in general are acclimated to supporting and validating men's feelings, it's going to keep encouraging this sort of snapping behavior.
I agree, but there is even more to this part. The Nazi ideology was not just about superiority, about also about struggle between races for power and need to win that struggle. You have to fight for your own and prove superiority through military conquest and physical domination of other races.
For that to happen, you need certain kind of fighter. Ruthlessness and nazi really seen ruthlessness as virtue.
Empathetic male eager to share emotions is less likely to gain domination through violence. Or through manipulation, backstabbing, lying and all those things that are seen as practical tactic by white supremacists. Less likely to push knowingly for laws that harm minorities or political opponents. Less likely beat or kill opponent. Less likely to force own friends into compliance with own ideas.
By that I want to say that the aggressive masculinity is virtue and something you want males to be, if you have aggressive goals. Hence peer pressuring males to be like that.