I've been chat banned a few times (nothing racist or sexist) I understand what valve is trying to do. However, I feel there is a disconnect between punishing a reaction to poor play and not the poor play itself.
Last night I had a game where a team of three got tired of playing after 45 minutes. They started to feed so the game will end. I called them morons repeatedly. I have little to no doubt that they reported me. So while I may not be banned from chat when I log in tonight I have to imagine that with my history it certainly is not going to help. Also as others have mentioned if I am banned it will hurt my future teammates more than anyone else. They can spin the numbers as they like, but I'm not sure how affective they have been in solving any of the issues.
Speaking on the first part only, bad play isn't and shouldn't be against the rules.