Why are some religions so serious about no sex before marriage?Watch
Either way, I don't see a problem with sex before marriage. Hell, I've already crossed that line
Sometimes the no sex before marriage attitude is intended to promote social stability, traditional values and a sense of personal responsibility.
My mother was brought up to believe in sexual abstinence until marriage and still does.
Fans of the abstinence movement often also have issues with divorce, single parents and birth control.
However, like said in above post, it's likely to have evovled for the benefit of simpler society whereby making people less likely (frowned upon) to go around having children outside of marriage. To ensure the children had high survival rate it would have been very important for parents to be dedicated - IE married ones.