This is patently false. Every man and woman has the natural law written on their hearts. Only the morally blind think, for instance, that killing innocents is good. Moral relativism is the enemy of a free republic. If good and evil are relative, then there is nothing stopping the State from doing what it pleases. If you want to read a full-blown refutation of relativism, I recommend Peter Kreeft's _A Refutation of Moral Relativism_.
Please offer proof that only spouses have the right to sex.
I did, when I said "They have this right because they have already vowed themselves to each other in a gift of self. The act of physical love is the consumation and highest expression of this full gift of self. Spouses' very body language in the conjugal act speaks marriage."
The burden of proof is on you to show that fornicators have this same right.
Fornication that does not result in a pregnancy obviously does not lead to illegitimate children.
But it runs the risk, and such a risk is morally unacceptable. If one has to choose between possibly damaging a child and not damaging one at all, and the only cost to you is the deprivation of a few minutes of pleasure, which is the rational choice? Not damaging a child at all, obviously.
Please offer proof that fornication is an unguided passion, and that a willed commitment is necessary for a man and woman to be satisfied.
You did read my post, right? I said it right here: "Though their[fornicators'] bodies speak the language of total self-gift, they do not give themselves totally to each other by an act of willed committment. Thus they are inconsistent and irrational."
The lynchpin of my argument is that sex is about total self-gift. I say this because of observations about what happens during sex: the woman gives herself to the man, and the man gives himself to the woman. If you want to say something different happens during sex, I'm all ears.