In Shadow's defense, I had witnessed people arguing with him/her, when none of them got banned for the arguement. Some people just want to start arguments when they say things like "Oh, you play spy? It must be SOOO hard to deadring everything." "You use (insert wep here) thats for noobs." These people look to start arguments with others. I did hear Michael warn about bans, but Shadow is not the only one to blame here.
Oh sure, people are assholes in tf2 sometimes, and when they reach a ceratain threshold when I'm around they get banned. Nobody else was being particularly bad at the time of this incident, he dug his own grave.