Bugbear » Sex is not a sin. Sex is something necessary to keep life going on. All creatures do have sex. Some are homosexual, some transgender, some Bisexual? There is nothing wrong with sex, unless your sex -desires hurt or harm your partner. I agree that some sex acts ex. pedophilia, violent Sadism, rape and so forth will harm your partner….therefore not acceptable. But as long as both or more agree fully….we should´t interfere with what other people do in their privacy…
A "sin" is an offense against God, and unless you're authorized to speak for Him, your answer is moot. There also seems to be quite a pantheon of gods on this world, so there are conflicting beliefs regarding His nature, disposition and will. And many seek to regulate sex as a moral issue, which makes sense. Sex has played a significant role in wars, murders, disease and a host of other evils in society. It affects future generations and cultures and sexual acts can go from normal and healthy all the way to disgusting and degenerate. According to Robert Graves, the Roman emperor Tiberius left Rome to reside in Capri, simply because in Capri he could engage in his own debauchery away from the prying eyes of his countrymen.
Fifty years ago, people "knew" homosexuality was wrong. There was virtually no social debate about it, and it was considered a sexual anomaly like pedophilia. Now there are groups saying that pedophilia is not an anomaly at all but a normal way to show love and affection.
To say there are no sexual sins is to say there is no God, which is also to say that if there is no God, there is no right or wrong. But I think most people know in their gut that some sexual practices are just plain wrong, and others are far worse.