>>40510559 (OP)You are correct, sex is not sin to God. Sex is needed to procreate after all. Sin is a sin and sex, due to its pleasurable nature, can easily become sin through lust.
Just as eating is not a sin, but gluttony is!
Sin lies in the purpose of heart and mind. Sex with your married spouse is not a sin, but adulturous affair is a sin even if both enjoy it.
Sex becomes sin if it becomes purpose and idol on itself just as nearly everything can. If you lust other people without repenting that thought immediately, you have already committed this affair in heart and mind. And God sees our hearts and minds, clearly. Our purpose.
Understand that condemning wanton sex is also to protect us and our self-worth (because enemy wants us to think ourselves as filthy monkeys and animals). Every human is a child of God with inherent dignity due that, equally valued in eyes of God. Sex that reduces other partner into an object, mere tool of pleasure, is sin. And has historically been very real threat due to power-dynamic of slavery, indentured service, feudalism and poverty. Porn in modern day is similarly a sin because it objectivies another child of God.
If there are two gay persons who love each other and are in committed relationship with each other, is this a sin? I do not know. My heart says no if they truly love each other and stay loyal to their bond. Of course, they still need to be christians and give themselves to Jesus to be saved like everyone. In that case, do they not shoulder each mother's crosses, too heavy to bear alone?
But if they claim such union is what God intended for humanity and try to change word of God or Church due to their own desires, that is a sin. Promiscuity is a sin for everyone. And gay relationships can more easily become sinful due to proclivity to sinful sexual practices (objectifying, hurting) and promiscuity.
Sin us sin because it hurts us emotionally, spiritually and separates us from God who is Love and Righteusness.