I call your one 'variance in opinion' and raise you one deviance FROM moral absolutes. And if I may be permitted a bit of word-play, every standard deviation is a slip down the slope.
Yes. Moral absolutes exist.
However, the variance of opinion still makes it necessary despite the moral absolutes on the subject. Heck, the moral absolutes come into play when formulating and codifying such a definition.
Moreover (and rather sadly), society can't agree on the very principle of moral absolutism, therefore, it's all the more critical to come to a consensus as to what's considered obscene.
As conservatives, we ought to be taking that bull by the horns...