Do y'all genuinely not understand why some people like chastity? Part of morality is interacting with sacred things only in highly ritualized contexts and focusing on strong emotions appropriate to the thing. Sex is sacred. If people have sex because of pious zeal to follow the first of all commandments, of deep hope for a child to birth and raise and love, and of overwhelming, passionate, committed romantic love that they have freely chosen to be bound by for life, then it's moral. If they have sex because it sounds like fun right now, then it's profanation and therefore gross/evil. Sacredness looks like a cultural universal. I like the theory that we have a general sense of things being in the wrong place that causes revulsion because it's a disease prevention mechanism, but it seems too narrow to hold water; it's good for avoiding dangerous food and contamination, but I can't see why it could affect sex, unless it was specifically triggered by STDs or something. (Now if someone could explain to me why so many people find gay kisses gross...)