What a lot of people don't understand about the WBC is that it has nothing to do with beliefs. I doubt Phelps actually hates gays as much as his websites would indicate. The WBC is the way it is purely to make money. They basically troll in the real world, where instead of getting angry replies, they get a punch to the face. They then sue their attackers for millions of dollars. This little girl is a target because protesting her funeral will create massive amounts of publicity and anger, which plays into their hands. It has nothing to do with God punishing the USA, that's just a cover story that most of us fall for. When they have decent, non-violent people calling for them to be killed, they've done their job.
Now, does this mean I don't want them to be killed? No. Hell, if I had the means, I'd do it myself. But these people are not religious fanatics, they're just consumed by greed. They protest funerals for the same reason Bernard Madoff ran a ponzi scheme; they want money, and they don't care who they have to screw to get it. Those of you commenting on how absurd their beliefs are, you might as well be using reason against an internet troll. The beliefs don't matter, they're just a means to an end.