I've been to a few counter-protests against Westboro or some of their copycats. Always fun!
In the US, the 1st Amendment exists to protect the speech of people like neo-Nazis, Socialists, Birthers and the Westboro Baptist Church. Our opinions on, say, DmC aren't exactly controversial and will not spark riots, but the speech/actions of the aforementioned groups could. Does that mean they shouldn't be able to say what they want, when and where they want? No. It means they definitely should. And this is coming from some one who has actively shown up to offer a contrary message at said groups' protests.
Should they actually crash a funeral or other meeting/service? No, that would be trespassing. But they can and should be able to go to nearby public places and let their voices be heard. By no means do they have a right to an audience, but they do have a right to talk.
If you add a "but" to any of that, you're adding a "but" to your own speech. I hope you don't have anything anyone would find controversial to say, because that's the kind of stuff that bites you in the ***.