I'm guessing religion.

Leviticus 18:22:

Do not have sexual relations with a man as one does with a woman; that is detestable.

Leviticus 20:13:

If a man has sexual relations with a man as one does with a woman, both of them have done what is detestable. They are to be put to death; their blood will be on their own heads.

Jude 1:7

In a similar way, Sodom and Gomorrah and the surrounding towns gave themselves up to sexual immorality and perversion. They serve as an example of those who suffer the punishment of eternal fire.

Referencing:

Genesis 19

Genesis 19:5–8

Before they had gone to bed, all the men from every part of the city of Sodom—both young and old—surrounded the house.  They called to Lot, “Where are the men who came to you tonight? Bring them out to us so that we can have sex with them.”

Lot went outside to meet them and shut the door behind him  and said, “No, my friends. Don’t do this wicked thing.  Look, I have two daughters who have never slept with a man. Let me bring them out to you, and you can do what you like with them. But don’t do anything to these men, for they have come under the protection of my roof.”

And:

Genesis 19:12–13

The two men said to Lot, “Do you have anyone else here—sons-in-law, sons or daughters, or anyone else in the city who belongs to you? Get them out of here, because we are going to destroy this place. The outcry to the Lord against its people is so great that he has sent us to destroy it.”

And:

Genesis 19:24–25:

Then the Lord rained down burning sulfur on Sodom and Gomorrah—from the Lord out of the heavens.  Thus he overthrew those cities and the entire plain, destroying all those living in the cities—and also the vegetation in the land.

Romans 1:26–28

Because of this, God gave them over to shameful lusts. Even their women exchanged natural sexual relations for unnatural ones.  In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. Men committed shameful acts with other men, and received in themselves the due penalty for their error.

Furthermore, just as they did not think it worthwhile to retain the knowledge of God, so God gave them over to a depraved mind, so that they do what ought not to be done.

1 Corinthians 6:9–10

Or do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor men who have sex with men nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.