Progressive Politics

The line could easily be drawn at "not calling for genocide" I think that's fairly safe.

The problem is that you don't get to draw the line; you only get to erase the previous line and mark the general vicinity where the next line might be.

So I don't see how banning Nazis speech will make things worse.

There's always room for things to get worse. Hate speech laws in particular tend to be pretty draconian so they've got a lot more room for things to go wrong than anti-terror laws (which, as you said, are already abused).