A sin is an act against God*. To act against God, one must perform an action contrary to his values. Many say homosexuality is a sin because God values only love between opposite genders. Today, I will demonstrate how the Christian perception of God dictated that he supports homosexuals and, therefore, homosexuality is not a sin. (God, for now on will refer to the God preached by Christianity)
God, according to Christians, loves people regardless of how their birth conditions; namely, God loves people whether they're born healthy, blind, deaf, mentally incapacitated, with a damaged heart or lung, with erectile distinction, sterile, or with schizophrenia. God doesn't judge you for circumstances beyond your control, including the conditions with which you may or may not be born with. The logic behind this preaching is sound; if a supposed God genuinely loves his children, than how could he punish them for something they had no control over, for something they coupdnt possibly have control over, for something that happened before they were even born?
Well, whether you want to believe it or not, it is a fact that sexuality is decided in the womb. In one study discussed in my high school AP Psychology textbook, researches isolated a protein responsible for the outcome of a monkey's sexuality. If this protein was removed while the monkey was in the womb, it would be homosexual without fail. The opposite occurred if the protein was present while the monkey fetus was in the womb. While not ethical to alter an infant's sexuality without their consent (which is impossible to obtain from a fetus), nearly identical proteins are found in the human fetus. This is why identical twins can have differing sexualities, because one fetus has this protein and the other does not.
If God loves people for who they are regardless of birthed conditions, how can he judge people for their sexuality, whether heterosexual, homosexual, or bisexual, if its determined before birth? People can't choose their own sexuality, so how can they be blamed for it? God cannot punish someone for something beyond their control, and this includes sexuality. Christians preach God punishes or blesses people for their choices. Sexuality isn't a choice. Therefore, God doesn't bless or punish people for any sexuality. Therefore homosexuality is not a sin, or act against God, because God doesn't punish people for for what they're born as. Now, once again (read my other articles), I ask, if people preach they need to be like God, and God doesn't treat homosexuals differently or call it a sin, then why do his followers?
*Atheists say there is no sin because they believe there is no God. How can one make actions against an imaginary being? Saying there is no sin does not mean atheists don't believe in wrong and right or moral behaviors. It just means that they don't believe in acting against and unreal being.