While a parent may strongly believe that one should wait until marriage to have sex, forcing a child to follow that restriction can result in a number of problems. Besides the obvious problems of sexually transmitted diseases and unwanted pregnancies, a bond can be lost between parents and their children. If children have to sneak around because of restrictions, they will be hesitant to share things with or their parents. What they hide may not be restricted simply to their sexual activity either. They may become increasingly silent about more issues in his life.
Silence leads to desperation.
Instances like killing a newborn and dumping his or her body in the Dumpster behind a motel or letting a disease go untreated and sustaining lasting health problems because of it can occur. While parents aren't exactly going to urge children to have sex, many times they understand how they are feeling and are willing to help. This doesn't excuse teens from responsibility though. If you are ready to have sex, by all means do something about it. Often times talking to a parent is a good start.