From John Roberts' eloquent majority opinion:
Westboro believes that America is morally flawed; many Americans might feel the same about Westboro. Westboro’s funeral picketing is certainly hurtful and its contribution to public discourse may be negligible. But Westboro addressed matters of public import on public property, in a peaceful manner, in full compliance with the guidance of local officials. The speech was indeed planned to coincide with Matthew Snyder’s funeral, but did not itself disrupt that funeral, and Westboro’s choice to conduct its picketing at that time and place did not alter the nature of its speech.
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. As a Nation we have chosen a different course—to protect even hurtful speech on public issues to ensure that we do not stifle public debate. That choice requires that we shield Westboro from tort liability for its picketing in this case.
It feels weird to be cheering a win for the WBC. But in the end this decision shields not only the WBC, but also war protesters, or environmental activists, or same-sex marriage supporters. This "different course" Roberts speaks of has to protect all of us -- or it can not safely protect any of us.