Mankind has a foundation for moral law. That foundation God: he God exists, and he created the world, people, and all things; God set up rules for the safety and well being of creation. Without God everything is relative to culture and personal opinion and there are no moral obligations. See the various commands in the Bible. They are valid because God is the creator, the rule maker, and he knows what is righteous and best for his creation
Therefore we need to know what God says about homosexual activity. God in the Bible forbids homosexual activity. I note just a few Scripture verses (Leviticus 18:22, Leviticus 20:13; Genesis 19, especially 5-13; 1 Corinthians 6:9-10; 1 Timothy 1:10; Romans 1:24-28). Clearly homosexual activity is sin. The person who engages in this activity is a sinner, just as every person who violates God’s will is a sinner. We should be thankful that Christ Jesus came into the world to save all sinners regardless of the sin.
Leviticus 18:22 and 20:13, abomination, תּוֹעֵבָה=to`ebah. Used 23 times. Other illustrations include Exodus 8:22 where the word is used two times, and in Deuteronomy 17:4 the word is translated as detestable thing.
Romans 1:24, impurity/uncleanness, ἀκαθαρσία=akatharsia, filthy, dirty, ceremonial impurity, depravity. See especially Romans 1:26-27.
1 1 Corinthians 6:9, effeminate, μαλακός=malakos, soft, weak, then passive in a same sex relationship. Homosexuals, ἀρσενοκοίτης =apsenokoites, intercourse with a man as with a woman.
Timothy 1:10, ἀρσενοκοίτης=arsenokoites, intercourse with a man as with a woman.
God designed marriage to be between one man and one woman and homosexual activity contradicts this design (Genesis 2:18-24; Mark 10:6-8; Ephesians 5:32).
Paul’s rejection of homosexual activity is not based on a cultural value of his time that would eventually change. Homosexual activity was as widespread then as it is now. He went against the culture. He based his statements on God’s design for marriage.
Homosexual activity is self-destructive. It promotes compulsive promiscuity, drug use, mental trouble, damage to the body, and disease. The media promotion of homosexual activity ignores these side effects. (Thomas Schmidt, Straight and Narrow, IV Press, 1995).