No one wants guilt by assocation, but Obama's pastor, Jeremiah Wright, isn't easy to ignore. Obama has said he doesn't agree with everything Wright says, and has recenttly strengthened that statements, but is that good enough?
Wright has said vile things in his sermons, on a regular basis, for quite a few years. Inexcusable stuff, I'd say. This is a church Obama chose, and chose to stay with. He even seems to be close to the Reverend.
I'm certainly not demanding every friend and moral leader pass a test, but if I supported a candidate whose church leader said something like, say, America was punished on 9/11 because we support homosexuality, I would want to know why the candidate belongs to this church. At the very least, I'd demand he publicly disavow those particular statements. I don't see Wright's statements as being any better.