The crux of the matter, it seems to me, is simply that the Bible has no sexual ethic. Instead, it exhibits a variety of sexual mores, some of which have changed over the thousand year span of biblical history. Mores are unreflective customs accepted by a given community. Many of the practices that the Bible prohibits, we allow, and many that it allows, we prohibit. The Bible knows only a love ethic, which is constantly being brought to bear on whatever sexual mores are dominant in any given country, or culture, or period.