If a belief system can compel you to supress natural sexual drives, it can control every aspect of your life.
The problem with creating an artificial boundary "sex is reserved for people married to one another only" is that unmarried people - virgins - have this expectation that sex will be plentiful with a spouse, because it was completely absent prior to marriage. As well, it places pressure on people to marry too soon - not wanting to fall prey to sexual desire - and the couple might well be miserable because they really weren't that good of a match after all.
It also allows for false value to be attributed to the virginal state, comparing it to a new, never used "something" (car, house, etc.). The first sexual experience can be scary and traumatic and disappointing - it gets better with experience, of course - but good sexual experience should be compared to a diamond or precious metal that doesn't lose its value over time, rather than being something worthless and shameful.
My 2¢, YMMV.