"Give them power" is really the key phrase. It doesn't matter what someone else says if you don't listen, can avoid them, and refuse to take what little you do hear to heart. They make one of the worst days in a person's life that much worse, which is inexcusable, but not justification enough to tear a hole in freedom of speech that could easily be used to silence legitimate, necessary speech in the future. Even if you don't believe that will happen, remember that with every concession we make freedom erodes. That isn't to say we shouldn't ever consider restricting freedom (that would be a slippery slope fallacy), but you have to weigh the pros and cons in each instance.
I just don't see how anyone can claim that it's worth risking freedom of speech to silence some nutjobs who become more and more hated with every public appearance they make.
Now if you want to talk fair, legal repercussions for what they do, how about we take away their tax exemption? That merely requires the law to be enforced, not bent or perverted. Political organizations, even if they have a religious basis, still have to pay the IRS.