Abstinence only might work for a person, but it certainly doesn't work as a model. You can't teach it in schools, because every time it's tried people come out unacceptably ignorant of the inner workings of the human body... and sometimes pregnant. You can't rely on it in society, because people don't care. Abstinence as a societal model has been field tested time and again and has failed every time. Because people want sex. It's hardwired into us. Abstinence only supporters ignore that and try their damnedest to "beat" sex, which is not a fight anyone can conceivably win.
I imagine you don't care about that. People having sex isn't their own problem, yeah? They made their decisions and have to live with it. But that's short sighted. There are MAJOR issues involving sex that people just don't want to talk about. Teen pregnancy, overpopulation, disease, and of course abortion. And in all these cases cheap and easy access to contraceptives/condoms have been shown to help the situation greatly.