I haven't yet read the judgment of the US Supreme Court in this case, so I can only go on various reports, including a quite thorough Wikipedia article (which will, I don't doubt, grow in detail).
This is another case of religious fanatics demonstrating ... with legal repercussions. But on this occasion they ultimately prevailed by 8-1 (Alito J. dissenting) at the level of the highest court. It was found that their speech was constitutionally protected by America's First Amendment. The case involves, of course, the notorious Phelps family and its habit of picketing funerals for US servicemen in order to make their loony (oh noes, the snark-hunters will be after me again!) point that America is doomed because of its tolerance of homosexuality.
Loony or not, it's a point that the Phelps clan are lawfully entitled to make. Should they have been entitled to make it in the way they did? Without having all the detail - so I could change my mind, I suppose - my answer is "Yes." Yes, based on the facts as given in the Wikipedia article. In particular, they abided by lawful instructions from the police and did not conduct their protests (or whatever) in a way that disrupted the funeral concerned. Indeed, they were at sufficient distance that mourners were not necessarily even aware of them.
On these facts, I don't see how there was even a case to be argued. The matter should never have gone as far as it did. That's not to say I'm sympathetic to the Phelps clan - on the contrary, I have nothing but contempt for them, and I have nothing but sympathy for the mourners. But unless I'm missing something important, this is a clear-cut case where the litigation should have been thrown out from the beginning. Litigation is not the answer to every evil, and the US Supreme Court has done the right thing in reinforcing that message.