Everyone loves cheeseburgers, well, okay not everyone. For instance, I don't really love cheeseburgers. But, the point remains that most kids love cheeseburgers and if you keep them thinking about cheeseburgers then they won't have sex. If they eat cheeseburgers, then they won't have sex. If they don't have sex they won't catch STDs.
So simple that it is the hypothesis upon which $1.5 BILLION in abstinence-only sexual education is based. Unlike the cheeseburger hypothesis, which would actually take into account how kids think, abstinence-only is a complete failure.