The analogy doesn't fit I realize now, because the teenager in the situation was fine until the bullying, whereas the victims are already grieving.
Also, burning the flag and wearing a "fuck the draft" shirt isn't actually aimed at people anyways, so that's not comparable. The Holocaust one isn't comparable either since there are many WBC members, not just one guy; the Holocaust happened a long time ago, so the victims have had time for their emotional wounds to scar; WBC targets individual people and families, whereas a Nazi parade is for an entire town; people can ignore the guy in the Nazi suit; and the Nazi is only marching in his uniform, not shouting about his views or trying to get attention.
If a gay kid was bullied in school and then commited suicide, and people at the school wore shirts that said "Fag deserved it" and "Fags go to hell" and followed around the student's siblings while yelling about how their brother was a fag who did all sorts of awful sexual acts(in detail) at them, should that be legal too? Even if it's only a day, do you think that should be allowed?