As long as it was just the launcher, there is no violation. That said, IF they had the rockets to go with it, I think that the BATF would be all over it. Of course, we ALL know that they'd rather prosecute religious people that are isolated in a compound or people who saw off shotguns a little too short by 1/2" or other domestic terrorists.
I have a little problem with the jihadist writings, BUT, the 1st Amendment protects even the most vile of writing or speech. We don't have to accept it, but we are obligated to tolerate it. I would HOPE that these people would be watched VERY closely.