Government DOES have a key role in determing what is right or wrong in our society. The "legalizing" or public recognition of "gay mariage" would mean that "We the People" have sanctioned this "union" by allowing it to take place.
Only for as long as 'We the People' persist in thinking that registration somehow also confers everyone's moral or religious approval. I suspect that most of the same-sex couples out there would simply point out that they didn't ask your opinion in the first place.
At any rate, my own view is that you and every other private party, whether individual or organzational, should be free (as for the most part you are now) to refuse to recognize any such union for your own purposes.
FWIW, I don't claim to "recognize" every heterosexual mariage that takes place, however I do recognize, as do most Americans the institution of mariage, and its definition, as being ONE man and ONE woman.