The issue comes with the phrase, "but not at the cost of injuring others." Libertarians don't believe you can harm the culture, only individuals within the culture. I strongly disagree.
I can only hope you're being facetious. If I engage in a behavior that harms you, that's immoral. If I engage in a behavior that harms me, but not you, that may be stupid but it's not immoral.
The moral law defins what is. There is one, and you have admitted to it. Something is immoral because it is, not because it meets your or my definition of immoral, nor even some Church's.
The moral law is generally attributed to G-d because social interactions are too complex for people to understand. G-d's revelation is required because G-d is the only one who fully understands humans and their social interactions. He did not give the moral law just so the faithful could have something to follow, but to protect us in societies that would allow the maximum of life, liberty, and the pursuit of happiness.
Whether homoerotic behavior violates the moral law comes back down to the libertarian fallacy that only individuals can be harmed. Our society is destroyed when it no longer celebrates self-control for the good of the whole. Homoerotic behavior is the poster child for self-satisfaction regardless of the whole. As I said before, it is not the only step on that slope, but it is one of the last.
Let me make this case another way. Suppose abolition had failed and blacks were still slaves in America. Suppose that you and I, being principled moralists, refused to own slaves or associate with anyone who did. Should we care that others own slaves? Should we ask the government to intervene and stop the immoral practice? If so, why?
Shalom.
That's not necessarily true, otherwise atheists would have no sense of morality, no guidance as to right and wrong. Surely you're not making that claim, are you?
Suppose that you and I, being principled moralists, refused to own slaves or associate with anyone who did. Should we care that others own slaves?
Of course. Ownership of a human being deprives that person of their rights and their self-determination. That's not a valid comparison at all.
We're going to continue to disagree.