Having lived what Yendu explains, I can tell you that it is freedom he teaches. Sin is the bondage you throughly describe.
Lowelljr is right. Those things that are considered sinful by Christianty (and most of the world's major religions) are things that we are tempted to, but which in the end are quite likely to subtract from the overall happiness we might otherwise experience in life. It is hard to see that - especially with regard to things like sex, where (particularly for men) the temptation can be extraordinarily strong. And it is much harder for the young to see that, because they haven't experienced the downsides that usually come, sooner or later, from sinful behavior. That is why, when one is fortunate enough to have loving parents, it is especially prudent to listen to them and to consider that the sometimes difficult messages are given in love. The same for the messages that come from relgious people. Most such people aren't out to impose anything on anyone. They're out to try to help people lead happier and more fulfilling lives.