For the most part I agree with Blow, though I would definitely still describe myself as left. Just because some who also identify as left behave in a bad way, I don't change my political opinion).
It may be clearly defined what a fascist is, but to identify humans as such is a more difficult matter. And being of a different political opinion should never be reason enough to be violent. If Milo or anyone else harasses people - and I think in this sense, the US' view on freedom of speech is to broad - he should be prosecuted, but in a lawful way. If you start to protest against people, not even people of power, but ordinary people, in a violent way to take their voice away. This way you may make yourself feel better, but I seriously doubt anyone will say "Oh, so if those people violently protest against another person who just wants to speak, then they must have a more rational view of the world". In political discourse it should be your aim to convince people on the fence of an idea, not to threaten people for having the wrong ideas. The latter position will backfire, if you do not happen to be incredibly powerful (and even then it might prove problematic).