I used to play on a few Day of Defeat: Source servers, and I met a ton of great online friends there. That's because they were dedicated and moderated servers that kicked and banned people for being assholes, in or out of voice chat.
But... If you're confident that you're never going to see the people in your match again, it's way easier to be assholes to them.
Yes but ..in a way it's when everyone went into their own private parties things changed as well. Removed some of the outreach you got with online gaming, especially team based one. Everyone's in their own chat bubble
Edit: someone below me said "impersonal" and that's the best word I can describe