I dunno... I'd say that the position, "I view this person's opinions to be such a threat that they should be killed" really is rightly seen to be a significant part of the problem with fascists, so it is a position I can't take, and that I don't like to see people with whom I otherwise agree take.
I think it's near certain that throughout history, the most harm hasn't been done by people who were knowingly evil, but by people who were absolutely convinced that they were good, and that they were fighting against evil.