If they can't control what they do with their bodies, they should be rounded up and treated like animals, because that's all they are. It might be an innate inclination, but it is still a choice to accept and act on that inclination. The moral options for a sincere heterosexual man are maybe a hair more expansive than for a homosexual, but his innate sexual inclination is never considered an excuse for stepping outside those boundaries.

Debate whether or not the choice they make is moral until the cows come home, but desist this farce of pretending the choice is not being made.

And that is the only acceptable way to realize that? This is absolute nonsense, and reveals a preference for, and idealization of, the homosexual cause. Marriage is a private arrangement between two people and the extent of the feelings and interests of the people involved therein are not for another to pass judgment on. The legal status of marriage, on the other hand, is a public issue, because of the explicit meaning given to the institution by tradition. Extending legal rights to other forms of marriage forces people who do not recognize those parameters to treat them as such, in violation of their own beliefs.

It is as absolute as a belief in a god, that marriage has a specific and explicit form, and you have no more right to force a person to treat a same-sex couple as a marriage or a polygamous relationship as a marriage, than you have to force them to attend a religious service or perform a religious ritual. If you can't force me to recite a patriotic pledge to my country or tolerate people praying to a different god in a public school, than you sure as hell can't force me to recognize an aberrant relationship as a marriage.