There's a lot of fallacious thinking going on here. There's probably some sophisticated name for this type of fallacy, but I don't know what it is. Just because the attackers were wrong for killing innocent people, doesn't make this hate video "right". False dichotomy, maybe?
Freedom of speech is about serving truth. It is an expression of the idea is that no one should be silenced for speaking about the truth. If someone is saying something demonstratively false, and that speech is endangering the public, then they should be silenced. This is the same reason you can't expect first amendment protection if you walk in to a theater shouting "FIRE".
So, to get this straight, speech is not protected by our first amendment ideology when it:
* Is demonstrably untrue
* Endangers the public
It's pretty easy to see that both of these conditions are met with regard to this video.