If this guy was some raving lunatic on a corner I wouldn't care. But he's got a country sized megaphone thanks to money and has also bought the government. So it does unfortunately matter that he's an insane christian cretin that wants to see the current form of government destroyed.

Because he made it our business by deliberately making it public.

Calling people "harbingers of the antichrist" is tantamount to advocating violence, not to mention slander.

If it's not advocating clear, specific and imminent violence (which this isn't) then it's free speech. You don't have to like it, in fact nobody is asking if you do.