You can't say that morals actually exist unless you have an objective basis behind said morals. Without God, I don't see how you can objectively even say that the Nazi Holocaust was wrong, let alone my position on homosexuality.
We don't need divine revelation or divine archetypes from any religion to establish moral principle and truth. I don't believe morals came from a vacuum, the morals we have are clearly from equal parts experiential knowledge, wisdom and reason in origin. Whatever creator, or creative processes exist, it stewarded us to developing these principles. The holocaust was wrong because it brought about the extermination of life and the suffering of individuals by standards detrimental to continued existence and civility. There are also innate human emotional reactions that have taught us no one wants that done to them. It's not just because the bible reports that God said "Thou shall not kill".
It's an incredibly far stretch to equate God as depicted in the bible to being the only possible foundation for moral standards.
I'm not sure I understand the question. God exists, so people who don't believe in him are still accountable to obey him and his word.
What I'm stating is, that belief in the Judeo-Christian God is not necessary to exist and have a peaceful, civil society. People today and throughout the ages have developed similar moral codes to Judeo-Christian ones. If you want people to accept your basis for the foundation of moral standards and invoke the word God, you have to prove the story of their advent depicted in the bible.
Can you prove that many cultures didn't come to exist civilly through morals developed from experience, wisdom and reason, especially the jewish tribe? I believe that is what they did, and then embellished it through mythopoetic thought.
In regards to homosexuality, I believe it was an abomination to them because it endangered survival of the tribe, by not having all possible members procreating. I'd love to see sound reason and proof of why that should be relevant today. Heck, homosexual behavior has been legal in Israel for decades and they stopped enforcing old laws a long time prior.
So why should any non-Christian accept your statement that they can't have moral standards to be true?