Homosexuality is considered a sin in many religions. But, from an atheist perspective, this is completely unnecessary and the persecution of homosexuals is unwarranted and immoral.
In most countries of the world, homosexuality and other deviations from 'normal' binary heterosexuality are frowned upon or worse. In many, such 'perversions' attract prison sentences or even the death penalty.
Leviticus 20:13 says: If a man lies with a man as with a woman, both of them have committed an abomination; they shall surely be put to death; their blood is upon them.
It is often said in reponse that Christians are not under Old Testament law and that the New Testament gives a different story. It does in that it doesn't specify the death penalty, but it still condemns homosexuality. Among passages doing so are:
Romans 1:26-27: God gave them up to passions of dishonor; for even their females exchanged the natural use for that which is contrary to nature, and likewise also the males, having left the natural use of the female, were inflamed by their lust for one another, males with males, committing what is shameful, and receiving in themselves the recompense which was fitting for their error.
1 Corinthians 6:9-10: 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.
So it does seem that part of being Christian is abstaining from homosexual relations (depending upon how literally one takes the bible). This is a restriction which Christians can place upon themselves, However, it is not a restriction for non-Christians. Despite this, many Christians expect non-Christians to live by Christian rules and accept the restrictions that Christians place upon themselves. They often justify this by saying that homosexuality will condemn people to hell. But, by Christian thinking, all non-Christians are going to hell anyway. Being homosexual won't make it any worse.
It isn't just Christianity which forbids homosexuality. Islam does too, as do other religions. And many religious people will prescribe earthly punishments as well as damnation in the afterlife.
Even in China, a country whose ways are not based on any religion, government sanctions discriminate against homosexuality. Why? Maybe because the thought of homosexual acts between men tends to be unappealing or even disgusting to heterosexual men.
If one takes the bible as the thoughts of men rather than God, then this might be the reason homosexuality was condemned from Old-Testament times. Note that lesbian relationships are not against Old-Testament law - presumably, because the thought doesn't disgust men in the same way. And religious texts like the bible and Islamic scriptures were written exclusively by men.
People who base their world view on observation, reason and evidence tend to see homosexuality and other non-mainsteam sexual orientations as part of nature (as homosexuality is known to be with many other mammalian species), and as not under voluntary control.
People who base their world view on divine revelation as contained in religious texts will more often believe that non-mainstream sexual orientation is a voluntary choice and often that the choice is made as an act of willful defiance against God, evidence that they are basically evil. People who begin to suspect that they are homosexual in adolescence are often quite distressed by it and try to convince themselves out of it, this strongly suggesting that it is not a choice.
In stark contrast to the situation 80 years ago, being homosexual is accepted by a majority of people in many Western societies and it might be expected that other non-theocratic societies will eventually move in the same direction. Because of the eternal nature of religious revelation, however, things will probably not change in theocratic societies. The spread of fundamentalist religions might lead to greater confidence in applying the full force of divinely mandated punishments to people who don't conform to the religion's expectations of sexuality.
Kiss: Wikimedia Commons