There is a compelling interest: providing children with a mother and father who won't bear retarded children. And that's a topic gays don't want to talk about because it means a state CAN regulate marriage when it comes to the wellbeing of children. Just not when it comes to systematically depriving them of either a mother or father for life..then "gay marriage is immune from state interference even if children will come to harm"..
It is the paradox that the USSC created when they removed the opposite gender qualification from a law that does not require sex as a requirement to enter into these partnership..
No paradox- other than the one invented in your own mind.