Does anybody actually read philosophy? Does anyone study ANYTHING anymore? First of all, "sin" is far too subjective a word to be used in this case. It is easily confused with notions such as right and wrong, good and evil. Sin implies an act prohibited by a particular religion. There are lots of religions. What is considered a sin in one is not in another. What was considered a sin in antiquity is now considered acceptable. If you want to pick and choose your sins, which many people do, fine. Just know that you have done so and be capable of understanding that as well as applying as much meaning as is reasonable to any act. Or, to be clearer, call homosexuality a sin all you want, but remember that wearing clothes of two different kinds of fiber, interacting with women who are menstruating, eating shellfish, doing work on Saturday, and working for a credit card company are also pretty sinful. If you're going to disregard your own sins and focus on the ones you like, fine, just be aware of your choice to do so.

As for right and wrong, the major moral systems, like deontology, founded by Immanual Kant, a staunch Christian, really forms no valid argument against homosexuality other than, "I don't really like it, it's gross." Well, you know what, I think eating beef is gross, but I'd hardly call it a sin. Let alone Jeremy Bentham and John Stuart Mill, founders of Utilitarianism, who have nothing much at all to say about homosexuality.

So, is homosexuality a sin? It depends strongly on who you ask and their biases, which they aren't likely trying to control. Is homosexuality wrong? Well, try taking ethics 101.