"Let me make one thing perfectly clear: I do not reject Christianity because of my desire to go around sinning without any guilt; I reject Christianity because I have closely examined its claims and I have found them to be unsubstantiated."
This sounds rather like something I posted in PP's comments some time ago. (Maybe it is.) But actually, upon reading this today, I realized that one of my reasons for rejecting religion is that I do want to go around "sinning" without any guilt --- if "sinning" includes such acts as doing work on Sundays, having premarital sex, and the whole host of other ordinary human activities that are arbitrarily prohibited by Christianity. It's an affront to human dignity to be forbidden to do something "just because", and that's a large part of what religions do.
One could argue that the prohibitions on ham and cheese sandwiches or tattoos are relatively benign (although still offensive in their arbitrariness), but when the control extends to things as important as people's sex lives, it becomes monstrous. We're on this Earth for a short and often lonely time. Physical intimacy answers one of our deepest needs: the need to narrow the gap between us and our loved ones, however temporary that narrowing may be --- as Rushdie writes in The Moor's Last Sigh, "defeated love ... is greater than what defeats it". To exhort people to forego sex without the blessing of archaic contractual rituals is no less immoral than telling mothers not to hug their children.
The Bible claims that the wages of sin are death. If you define "sin" as "anything prohibited by the Bible", I believe that the wages of sin are something far less morbid: happiness.