Personally, I agree with zorse. One of the best ways to combat extremism is to give extremist groups enough rope to hang themselves. Nail them when they actually solicit or request specific illegal actions (calling for hits on people, calling for somebodies home or business to be vandalized, etc) but otherwise allow them to make fools of themselves in public. See how the WBC or the KKK marginalize themselves in the US by being permitted to publicly say what they think.
Radical Islam does not seem to be a sizable threat in the US (because of, or despite of, the US's loose hate speech laws... you decide) and domestic "homegrown" terrorism is a wildly overblown threat. People like "sovereign citizen" are widely mocked using material that they upload to social media. Would sovereign citizens still be widely recognized as nutters if they were not allowed to upload youtube videos of them making fools of themselves? Despite (or because of) the US's lax speech laws, we don't have a Golden Dawn equivalent political party that is actually winning elections.