the Constitution protects a right to gay marriage
The Constitution protects all rights that are originally retained by the people:
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
If there is a natural right to gay marriage, the Constitution protects it. That is, the Constitution protects gay marriage to the extent that recognition of gay marriage is in some sense naturally required as a precondition of fostering "life, liberty, and the pursuit of happiness"; as are the rights to free speech and free exercise of religion, to self-defense and self-organized collective defense, and all of the other rights recognized in the U.S. Constitution. A natural right “is not a right granted by the Constitution. Neither is it in any manner dependent upon that instrument for its existence.” (United States v. Cruikshank, 92 U. S. 542, 553 (1876))
I like the Ninth Amendment too, but it's worth noting that the majority opinion in Obergefell v. Hodges cited the due process and equal protection clauses, not natural rights: one could argue that the rationale was absurd even if the outcome was correct.
Another month, another rationality quotes thread. The rules are: