This sort of a deep question, requires some beyond the box thinking. Recently, Pastor Rick Warren was comparing Gay relationships to what mainstream society refers to as perverted or at least kinky. One of those references to gay sex was "incestual."
Was Adam and Eves relationship that way. If they were the beginning of sex and mankind, were they not brother and sister? Who else was around in those days? I suppose we could allude to the fact they were separate entities, but who says, and that doesn't make sense. Are we one big dysfunctional family in this world?
What most overlook when taking exception to gay relationships, is that almost everyone has more than one sex partner. Call it adultery, fornication, whatever, but mainstream society seems to give monolithic perversions a pass, while attacking faithful gayness. It's very much like the good ole boy network of husband with a mistress, very acceptable. But not acceptable for a wife to talk of her lover on the side.
Righteous and pure is in the eye of the beholder most often and what Society deems acceptable. I for one, am a total believer in heterosexuality but also believe in virgin brides which seems outdated today. One partner for a lifetime, man/woman. But we must address scapegoating also and devising our own set of rules. It has a tendency to be smug and prudish.