Whether same-sex "marriage" should be legally recognized and whether homosexual acts are moral may be related but are, nevertheless, two separate questions.
Let's say that gin rummy partners want their unions to enjoy the legal recognition that comes with civic marriage. For that to happen, marriage law must be as indifferent to sex as gin rummy partnerships are.
Now it should be obvious to all but the most ideologically hidebound that opposing the re-definition of marriage for the sake of accommodating all gin rummy partnerships does not entail a pronouncement upon the morality of gin rummy. One can think that gin rummy is fine. One can even enjoy playing gin rummy (I do, in fact), but still think that the act of gin rummy cannot consummate a marriage and, thus, oppose gin rummy "marriage" without any commitment to the proposition that the game itself is immoral.