In the Roman Empire, BC, sex was pretty open....

My answer is that sex became taboo in the western world with the rise of Christianity. Yes, I blame that for the sexual repression of the western world.

Sex is a basic animalistic function like eating and sleeping; it is what we all want and need. Society, however, has artificially romanticized it, made it either dirty and filthy, which isn't true, or only between people who love each other, which also isn't true. It is for two people who are horny.