There is an excellent post over at the Unfundamentalist Christian blog on Patheos, entitled "The Spirit vs. the Letter: Biblicalism and Conscience".

Excerpt:

"The analogy is not that slavery and homosexuality are the same, a nonsensical argument that ignores the true issue. The analogy works precisely because those who so vehemently assert that the Bible unambiguously condemns homosexuality are the inheritors of the same methodology slaveholders used to justify slavery: namely, they pointed to the literal word of God, and rejected arguments that slavery was not in keeping with the spirit of the rest of the Bible, just as opponents of homosexuality today reject any argument from the Bible concerning love, justice, even gender neutrality, and demand explicit 'biblical' support for gay rights."

http://www.patheos.com/blogs/unfundamentalistchristians/2013/07/the-spirit-vs-the-letter-biblicalism-and-conscience/