AR,
The only thing I would say to you on that is Phelps is not a Christian he may have been at some point way back when he was a civil rights lawyer but he jumped the tank some time ago.
That's the problem. Who gets to define "Christian"? There are a lot of protestants who don't think Catholics are Christian, do we let them define? Do we let the Christian homosexuals say that people who don't like homosexual marriage can't be Christian? Or do we accept that homosexuals by definition can't be Christian? Can you be Christian and support the death penalty? Maybe Phelps cares so deeply about the danger homosexuals pose to our country that he is trying to protect us from damnation by ridding us of them (yes, warped IMHO, but the guy really believes he's doing the work of God).
I can definitely accept that their actions are not Christian in the way I see the religion, or in the way that you or any of my Christian friends see it. But then nobody gave us the power to proclaim with definitive authority who is or is not Christian (unless maybe you're a strict Catholic, then the Pope can, in your opinion).