For encouraging violent acts, yes. For encouraging hatred? Well, the point of speech is to have an effect on other people.
Speech which doesn't affect others is pointless.
So why were the Nazis successful? Was it because their type of speech was not banned? Or was it because they banned opposing voices, both explicitly and implicitly via threats of violence?
Anyone wanna learn from history? If you go read Freakonomics, you'll see the story of a reporter who helped destroy the net effect of the KKK by helping tout, and making fun of, their positions. Thus it turned into little more than a social club. (Something some idiots in recent days are trying to reverse, by the way, with talk of attempted bans.)
How do I get off this subgenius world? Sheesh.