The father of Marine Lance Cpl. Matthew Snyder sued Westboro, claiming that the protests amounted to harassment and infliction of emotional distress. But the Court held in an 8-1 decision that the Church has the right to promote its message. Chief Justice John Roberts wrote, "Speech is powerful. It can stir people to action, move them to tears of both joy and sorrow, and– as it did here– inflict great pain. On the facts before us, we cannot react to that pain by punishing the speaker." Justice Alito was the lone dissenter.
This was a tough case, but I agree with the Chief Justice. If the First Amendment didn't protect offensive (really offensive) speech, then what would be the point of having one? Content based restrictions on speech are a slippery slope. A better response is to drown out their speech with other speech.
The Westboro Baptist Church protested in my hometown a few years ago (at a funeral for four high school girls, no less), and the entire community was devastated. But the answer isn't to get the government to force them to stop. Just as they have the right to be disgusting and crazy, the rest of us have the right to disagree with them, loudly and vigorously.