Why do the Abrahamic religions call for repression of natural human sexuality?

[Ohmightysmiter]

Shared between two people who genuinely care for each other, sex is beautiful. When shared between people who aren't committed to each other, it's still quite fun.
So, what's the point?
The Bible prohibits fornication, aka sex outside of wedlock. There is no point to waiting for marriage. It only ensures that you'll suck at it.
Oh, and Marj, I was born just fine the first time.