I haven't used Steam Community Forums for a few years, but when I did, it really depended on the game (and I'm not the type to be playing the games where there those behaviours would become prominent). As someone who mostly plays indie games, I found the odd racist post where it was clear they were trying to find like-minded people and nobody would bite. Also, if I reported something for any reason, they typically took care of it within 24 hours at the most and I never had a case where I reported something get rejected.