There are good reasons to ban certain speech. If people will give you money in exchange for your "cure for cancer" that is actually just tap water, for example. If you're condemning someone to prison. If you will cause unwarranted massive panic.
"That's offensive!" should not be on that list. Because, y'know, at that point you're playing the "how offensive is too offensive" game, and that's the game were you win by being as overly sensitive as possible.
I'm not saying that the families of the people whose funerals the WBC pickets are being overly sensitive, of course. They are completely right to find it disgusting and appalling that someone would do that. But if the WBC is banned for being too offensive, that's the very point were "offensive" becomes a valid reason to ban speech. And from there, it seems just too bloody likely that the next thing that is too offensive will be a book, or a religious view, or a political position. Hell, I'm willing to bet that every single person posting in this thread has an opinion that someone, somewhere, finds just as offensive as picketing a funeral. I know I do.
Of course, as far as I can tell, that's not what this petition would accomplish. It doesn't seem like it would actually accomplish anything at all, "legally recognised hate group" doesn't seem to be a real thing. But still, the arguments in this thread keep popping up every now and then and they piss me off every time.