Wow. Don't know where to begin. As a matter of fact most the world's religions and philosophies do not regard homosexuality as a sin (i.e Buddhism, Hinduism, all Jews but Orthodox, and a fair number of the liberal Protestant denominations). Also throw agnostics and atheists into that grouping, although we are not a religion.
Unfortunately all of the abrahamic religions acquired the stricture against homosexuality from the Pentateuch. Progressive elements of religions such as Judaism and Protestantism have updated their rational moral compass. Catholicism, Islam, Conservative Protestantism and Mormonism continue to live in the Bronze Age on this and many issues.
There are no absolute moral truths and sin is a human construct. We humans create our own morality, and it is far better today than that promulgated thousands of years ago. Not changing with the times is why religions are dying (thank god).