The slippery slope did not start with gay marriage, or even with the legalization of sodomy, but with legalizing birth control and abortion. The legalization of birth control changed sex into something sterile (just like sodomy). It led to, in the view of the culture, the separation of sex and procreation. Sex began to be viewed as something sterile. This first led to the normalization of fornication, and not long after sodomy. If sex is something that is done for pleasure, and has nothing to do with reproduction, well that can be achieved with a man just as well as a woman.