To start with, let’s get to the heart of the question. Christians (good Christians) don’t have venom and hatred against the LGBTQ community. They don’t support pushing the beliefs of that community onto society as a whole, that is true. And the more they are pushed to accept it as normal and okay, the more they will resist.
But the question goes on to list the 10 Commandments as the only list of things considered a sin in the Bible. It isn’t. And to be honest, the 10 Commandments are Mosaic Law (Laws of Moses) that were strictly Jewish in the beginning. Christians are the followers of the teachings of Christ Jesus. Jesus was the sacrifice of the new covenant to them. It doesn’t replace the old testament (including prophecies) but works with it and makes the laws actually attainable to man.
Then onto the meat of the question. Why do they believe it is such a sin? Because it is listed quite a few times throughout the Bible as being a sin in the eyes of God. It isn’t just once or twice. It is listed more than 25 times as being a sin. From the Old Testament to the New. It isn’t that the Christians are saying it is a sin, they see it as God telling them it is a sin.
And to tie it all together, let me relate a story our pastor used in one of his sermons. We had a woman that started showing up to church regularly. She kept to herself and sat in the back, usually slipping out quickly after the sermon. One Sunday she stuck around a little bit and asked the pastor if she could talk to him. He was glad to. He mentioned he had noticed her there on previous Sundays but hadn’t pushed to meet her. She told him she was uncomfortable in church because she was a lesbian and was pretty sure the congregation would hate her if they knew. His answer was very simple. He told her that there would probably be one or two that would avoid her, but that she was always welcome…everyone is welcome. He said that to be straight up, the Bible teaches us that homosexuality is a sin in they eyes of God. But he also told her that we are ALL sinners. It is the nature of humans to sin. It isn’t for us to judge her, that is between her and God. But he told her we are more than willing to help her have a relationship with God.
Maybe I’m wrong, but that isn’t venom and hatred. It is identifying a sin, yet accepting the person anyway.