I think you have to take the bad with the good when it comes to free speech, and any limits on it have to be very seriously thought about by lots of brains all far above my pay grade.
I'm not sure protesting a funeral or just saying "God Hates Fags" should be limited since while it is hateful, I'm not sure that being hateful in itself should be limited, but when the speech incites violence then it crosses that line. But different countries have different places they put that line.
I'm sure Westboro chooses their slogans carefully (as pointed out they're a family of lawyers), they don't have signs advocating stoning of homosexuals for example.
As for your case BigBrodieFan, I think the human wall idea is the perfect response. Engaging them just legitimizes them. Advocating violence against them just plays into their hands and harms us more than it does them. A human wall resists them but doesn't engage them. Feels like satyagraha