The WBC may be hate-filled bigots, but I do not think they're stupid enough to do something so blatantly illegal. What they will do is try to use that house to further their own agenda.
And as someone here has said, ignoring a problem does not make it go away. Rather, it can in fact exasperate the problem even further because what people like these thrive on is attention, and when they don't get it, they do something else, even more radical, to get it. Note I said radical, not illegal. A good number of these people are lawyers. They know how to skate right along the edge of illegal activity without actually crossing the line.