Cideon: For some reason your post got me thinking some odd thoughts that are in disagreement with you, but not really. Let's rephrase the debate some, in the comfortable terms of science fiction. Aliens come to Earth, and say that the good news is that they'll use their amazing technology to beam up dying people and keep them alive forever with amazing medical care (that only works in space, so no coming back to Earth, but they can meet up with other people beamed up). However, gay sex is just horrible, because. In fact it's so horrible the aliens refuse to beam up gays to get the free end-of-life medical care. Furthermore, they will punish places that permit the gays to do what they want. Awhile back they broke out the full lasers & brimstone for the sky treatment for Sodom City, but lately the aliens just intervene in more subtle and insidious ways, and they're still totally willing to kill everyone if it came down to it, because gayness is just that bad, and it's for our own good that they're discouraging us and bringing nations to ruin that disobey.
In such a scenario, you can credibly argue that humanity should adopt the party line because, well, the greater and more powerful force says so, and we don't want to have our cities fried by fire & brimstone. And to go against it is downright immoral, because it endangers the entire community. Anyway, the aliens are more powerful than us, they wouldn't forbid teh gayz without a good reason, just like a parent scolding their child to take the bad-tasting medicine. Who are we to question them? So... given this scenario, I don't think it's unreasonable to clamp down on gay rights.
The real world is weird because people disagree on if the aliens actually exist or not, and if they do, whether the aliens really dislike gays after all. But given that some people really truly sincerely believe the aliens will inflict terrible punishment on those who condone homosexuality, it's not an evasion or "I don't want to think too hard about it;" it's a serious matter of life or death! The more interesting question is whether such a powerful force that comes down and starts laying down such arbitrary laws is in fact worthy of worship and admiration, rather than the begrudging acceptance of a conquered people... but that's a whole 'nother can of worms.