The first thing that has to be established when dealing with this issue is whether the homosexual act itself is considered by God to be a sin. I haven't read every post in this thread, but I have seen posts supporting opposing views on this.
The main scripture I look at is what Jesus Himself spoke.
Matt 19:1-9-- When Jesus had finished this instruction, He departed from Galilee and went to the region of Judea across the Jordan. Large crowds followed Him, and He healed them there. Some Pharisees approached Him to test Him. They asked, “Is it lawful for a man to divorce his wife on any grounds?”
“Haven’t you read,” He replied, “that He who created them in the beginning made them male and female,” and He also said:
“ For this reason a man will leave
his father and mother
and be joined to his wife,
and the two will become one flesh?
So they are no longer two, but one flesh. Therefore, what God has joined together, man must not separate.”
“Why then,” they asked Him, “did Moses command us to give divorce papers and to send her away?”
He told them, “Moses permitted you to divorce your wives because of the hardness of your hearts. But it was not like that from the beginning. And I tell you, whoever divorces his wife, except for sexual immorality, and marries another, commits adultery.”
In the portion of the scripture I underlined, Jesus is quoting Genesis 2.
Gen 2:18-24-- Then the Lord God said, “It is not good for the man to be alone. I will make a helper as his complement.” So the Lord God formed out of the ground every wild animal and every bird of the sky, and brought each to the man to see what he would call it. And whatever the man called a living creature, that was its name. The man gave names to all the livestock, to the birds of the sky, and to every wild animal; but for the man no helper was found as his complement. So the Lord God caused a deep sleep to come over the man, and he slept. God took one of his ribs and closed the flesh at that place. Then the Lord God made the rib He had taken from the man into a woman and brought her to the man. And the man said:
This one, at last, is bone of my bone
and flesh of my flesh;
this one will be called “woman,”
for she was taken from man.
This is why a man leaves his father and mother and bonds with his wife, and they become one flesh.
Jesus spoke to this issue by going back to the beginning in revealing God's basic design for sexual relationships. Jesus made several essential points in this short scripture.
1) God created humans as male and female (not male and male or female and female) for the purpose of marriage and procreation.
2) Husband and wife (not man and woman) are to be joined in sexual union and become one flesh.
3) What God has joined together, man is not to separate.
This was God's design from the beginning. He made humans male and female. Man and woman are to become one flesh within the bonds of marriage. And marriage is not to be dissolved except on specific grounds because of what God designed and established from the beginning.
These scriptures show that homosexuality doesn't fit into God's design for sexual relationships. In fact, homosexuality defies the basic design of God, who commanded the first husband and wife, Adam and Eve, to multiply, i.e. produce offspring.
There are other scriptures that clearly show homosexuality to be a sin. To be sure, it's not the only sexual sin that people can engage in, but it is clearly considered an unrighteous act, and its practice keeps a person from inheriting God's kingdom.
1 Cor 6:9-11-- Don’t you know that the unrighteous will not inherit God’s kingdom? Do not be deceived: No sexually immoral people, idolaters, adulterers, or anyone practicing homosexuality, no thieves, greedy people, drunkards, verbally abusive people, or swindlers will inherit God’s kingdom. And some of you used to be like this. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.