If any person threatens another person specifically, the threatened person has the right to defend their live by any means necessary. So yes, if some fanatic threatens you specifically, I say that you have the intrinsic human right to self-defense, even if it means acting pre-emptively. Same goes for the country as a whole: Hostile states threatening the US should be fully aware that they will get what's coming to them.
That said, if a group is spewing random bouts of threats and hate, I say that the government does not have the right to shut them up. It is up to the people to drive them out of town. The government can certainly keep an eye on them and head off any attempts at actual violence, but it should not be stopping them from saying what they want to say, only from acting upon it. I don't care if they have Lou Horuchi sitting 300 yards away from the fanatics place with a rifle, waiting for them to try to act on their threats, but as long as they're just talking, they should be allowed to talk.
It is up to the PEOPLE to self-regulate what they will tolerate in terms of speech and expression in their community, not the government. This is why police did not exist in early America.