Gay "marriage" must inevitably lead to the demand for approval of all other forms of consensual activity and the demand that the state punish those who fail to bow to that demand. When you point this out, you get sneered at and told that believing in a slippery slope is utterly ridiculous. Then, when the guys who led the charge for gay "marriage" begin leading the charge for polygamy and group marriage, we are told that it is the obvious corollary to gay "marriage" and always has been. It reminds me of this. More here, here and here. Eventually, a culture that sees consent as the sole criterion of the good loses its capacity to conceive of a Common Good at all. And when the powerful in such a culture lose the capacity to conceive of a common good, it does not take them long to think to themselves, "Why then should I care about your consent if it gets in my way? I must Follow My Heart [which generally means "Follow my Will to Power"]. So let the strong do as they please and the weak suffer what they must."