Then they're breaking the code of conduct, and should have their accounts suspended. That's a lot better than letting them keep their reasoning silent.

It's not so simple, you can post snappy/disrespectful comments that skim the line and create an unfriendly atmosphere for a very long time.

It's a hard problem, because it's about patterns. Everyone has a bad day and posts a badly worded comment every once in a while; I certainly have. That's okay, it's human nature. The problems start when a small group of people do it all the time, and turns out it's rather hard to actually detect those kind of patterns.