Nothing would besides it would be idiotic for a Democratically elected Government to do so. If you want marital relations to be a Constitutional right you can pass a Constitutional Amendment that so specifies. You could include other bodily functions as well. But such a right was not spelled out in the Constitution and the right of privacy has to be derived from penumbras. If you give the Judges the power to divine penumbras you make the Judiciary a Perfect Tyranny.
Well, we have a clear fundamental philosophical disagreement, and this is one that separates those of us with a more libertarian view of the constitution than some of the religious conservatives here. I believe that, for instance, marital relations, being of common law origin, predate and are implicit in the Constitution, and I don't think that the state has the power to define what happens in the marital bed.
You might want to take another look at the 10th Amendment of the Bill of Rights... Just because a "Constitutionally protected right" isn't listed, does NOT mean it doesn't exist.
By your definition, then everything NOT listed in the Constitution might be made illegal, except when specifically exempted by law...
Mark