Well, I'm guessing that a lot of them choose not to believe that part of the Bible.

Reading the arguments that Meatballman linked above, it appears as though the root of the issue becomes translation from ancient hebrew. Their claim is that in most cases, the original words referred to a generic cult prostitute, and that only in later translations did the words take on meaning which referred specifically to homosexuality.

I think that digging down to the original root meaning like that is an important thing. If you've got an entire culture based around words in an ancient text, it would make sense to be sure you know what they really meant when they wrote it.

Whether or not their arguments about those particular translations are valid isn't critical to me, since I don't adhere to that text anyway (regardless of its translation). I was just curious where the philosophical justification came from, and that link has answered this curiosity to my satisfaction.