No one said that we should tell them to have sex. What I am saying is stop telling them to wait until marraige when it is evident that they will not. As far back as the Kinsey study, it has been shown that people have sex outside of marraige. With people waiting longer and longer to get married, to expect them to wait until marraige is unrealistic.
And, yes, we should tell kids that sex isn't bad....because it isn't. Why lie to them about it? All that does is make them not trust anything you say when they have sex and discover it's is pretty danged good, and you lied to them. And yes, it promotes responsibility if you let them know that they can come to you for assistance in getting birth control. You can also tell them that you would rather they wait until they are mature enough to handle the complications that being sexually active will bring into their life, but if they are dead set on becoming sexually active, you will make sure that they have what they need to protect themselves not just from unwanted pregnancy, but from diseases that can rob them of their life.