It would never be practical to enforce abstinence as a legal rule. However, I think we can do a MUCH better job at encouraging our youth to pursue sexual abstinence. We've made pre-marital sex look soooo normal, through our media and our over-sexualized culture in general, that when someone dares suggest abstinence we scoff at the very idea. Surely those impulses can't be resisted or reigned in; it would be absurd to expect teenagers and young-adults to exhibit some self-control! We've just accepted the idea that pre-marital intercourse is bound to happen, so we don't even fight it anymore. We barely even bother talking about abstinence in sex ed anymore; instead choosing to focus solely on the proper use of contraceptives. Now there's nothing wrong with contraceptives, but the best way to avoid unwanted pregnancies is by not having sex in the first place! If only our society taught that sex was meant for marriage, think of how many problems it would help solve! The number of unwanted pregnancies, abortions, ill-cared-for children, adulterers, divorces, and sexual crimes would all arguably drop significantly. Just take your average murder drama on T.V. for example. How many of those crimes are caused by uncontrolled sexual urges? The vast majority of the I believe. But most of our society will NEVER practice abstinence because, darn it, sex is fun. And if it feels good, why should we have to wait??? We can always just ignore the logic and pretend we know what we're doing, right?
(Yes, yes, I know some people are going to yell at me for drawing some of these conclusions. I'll explain my reasoning on whichever ones you'd like me to. I just didn't feel like making this any more long-winded then it had to be...)