Whether or not it is assur for non-Jews to live a gay life, we live in a country that votes on its moral issues. We are GUESTS here, whether or not we like it, and as such we don’t get to make the rules, in any meaningful sense. Use your votes to give yourself a voice, but ultimately, majority will rule. We do not live in a Theocracy, but rather a Democracy. And we don’t get to tell people how to live their lives, in spite of our disagreement with their abhorrent lifestyle. Not here, anyway.
BTW, this is the answer to why we need the Torah. When left to its own devices, society will alter its moral stance to suit the times. Only the Torah is constant.