Here's the problem. Not all people who believe in the Bible are homophobes. In fact, not even all people who believe that homosexuality is a sin are homophobes. As Luth has said, it is entirely possible for Christians of good faith to come to opposite conclusions as to the interpretation of the passages that condemn homosexual conduct.
Dan Savage's speech was broadly condescending and offensive to anyone who is a Christian. If I was there, I would have walked out too, which, by the way, is a perfectly legitimate way for someone to express their disagreement with the person giving the speech.
Dan could have gone about making his argument in a way that would have pointed out the hypocrisy of the Christians who have condemn gays while ignoring other sins. He could have pointed out that even if homosexuality is a sin, that fact in no way would condone bullying or discrimination against gays. He could have used the Bible to his advantage, and pointed out the instances where Jesus stands up and defends the bullied and the ostracized, even if they were sinners.
Instead he chose to be snide and condescending to everyone who believes in the Bible, and not just to those who use the Bible to justify their bullying of gays. It was a stupid approach and entirely counterproductive to the very admirable goal that he is working to acheive.