You are trying to make a biological fact into something arbitrary. To exclude sexual behavior from Natural Law can not be done. That is stating that man is not part of Nature. Our government was founded on Natural Law. As Cicero stated and our Founders concurred, justice can NEVER be decided by man's opinion, but only upon Nature.
The Founders studied other cultures extensively and found great fault with hedonism in the Roman and Greek empires among other cultures that glorified homosexual behavior. The rampant homosexuality and other sexual perversions led to an unjust civilization and to the debasement of women and children, who were also used and abused sexually and treated as slaves.
Studies in primates, etc., have shown that when you interfere in the natural process of animals raising their young, the young become pathological in many areas and are sexually abnormal.
Homosexuality is not genetic....it is a behavior that is caused by environment--mostly emotional and physical abuse--so by that logic, the behavior should never be elevated or glorified in any way. If it is, you are advocating child abuse. Sexual morality in religion and marriage were instituted to protect the man/woman relationship and to promote the healthiest environment to raise emotionally healthy children for the most successful future of a civil society. Their idea worked to the greatest degree ever for the most diverse population in the history of the world.
Why would anyone want to go backwards and copy the Spartans or the Nazi Brownshirts or the imperialist Japanese, in elevating behaviors that destroy the family of man in every civilization that nihilistic behavior was embraced.
I'm not sure how to reply to some of this but I'll try.
You begin by saying "You are trying to make a biological fact into something arbitrary." when I believe I am attempting to do no such thing. I referred to other arguments that other people have made - but those are other people and not me. I referred to liberals in an attempt to refer to their motivations. Referring to those motivations doesn't mean I share those motivations. I thought I even said I explicitly agreed with you about gay marriage.
That aside - I believe the idea that THEY are treating biological facts as something arbitrary is disputable. Some are but many are not. Liberalism is no more monolithic than conservatism. Or do you believe that your ideas would enjoy 100% support in these forums? Motivations play a vital roll in what they believe and why.
Now when you say that " Sexual morality in religion and marriage were instituted to protect the man/woman relationship and to promote the healthiest environment to raise emotionally healthy children for the most successful future of a civil society." you haven't actually disagreed with anything I said. That fits with the definition I gave of marriage as a sacrament instituted by Christ. If Christ elevated it to that position that means that it was other things at other times to other people. Else what did he elevate it from? Marriage is no more monolithic than conservatism. Even today there are cultures that permit chattel marriages, plural marriages, and even post-humous marriage by proxy. Are all these people sincerely pursuing these ideals acting out of hatred for and desire to mock Christians? I think not. Do we want to sway them to our point of view about these things? Certainly. Do we do so by ascribing evil and mockery to them when they have been attempting to live the best life they know? Hardly.
Your last question touches on what I was trying to drive at. You ask: Why would anyone want to go backwards and copy the Spartans or the Nazi Brownshirts or the imperialist Japanese, in elevating behaviors that destroy the family of man in every civilization that nihilistic behavior was embraced? Well .... that's just it. Usually they don't think that is what they are trying to move our culture to. Most of the time these people sincerely believe they are trying to move our culture to something much better than any of that. They are sincerely wrong and joined by a nihilistic and destructive minority that might well be pursuing those ends in a knowingly and wantonly destructive fashion -- but this is usually a very very small if very very destructive minority. If we judge the whole group by the worst of it's individual members and ascribe that worst motivation to all of them ... well... usually end up alienating them in such a way that people are no longer interested in hearing what we have to say. It's abrasive and they reject it. Rightly so since those are not, in fact, their motivations but rather the motivations of a smaller part of their number that they themselves may not even like.
Given that conservatism is, more or less, always running against the majority grain in any given time or place I think it's best to avoid abrasivness and mis-ascribed motives if we hope to get anything done.