Dogma is credal, gay marriage is not in the Niceane Creed last I checked. Neither is mortal sin (a concept that has evolved from the Book of James to Vatican II). Gay civil marriage and support for it is not a moral issue at all unless you consider defending equal justice undner law and preventing the tyranny of the mob (even religious ones) to be a matter of morality, which I do. The question is, why don't you? Not a stupid question. The natural law reason of Fagothy ended in a tie (meaning it could go either way, 335-340). He had to refer to Theism to break the tie, which essentially means a loss on reason and a win for authority (if authority wins such arguments, most real philosphers say no). Put another way, if all things being equal, reason is permissive (which Fagothy could not say in THE Catholic ethics text), then the Magisterium is in error on this issue and therefore capable of error on all issues (which is why Humanae Vitae is such a failure).