I would agree that if it the ***only*** program taught, then that is unrealistic, and yes, it could ultimately harm them.
Sex is a powerful topic though. It spawns emotion, it provides a multi-million dollar industry, it's responsible for medical bills for STDs and pregnancies. It makes the world go round.
There is no way to legislate what parents choose to teach their children about it, though. Common sense tells me that having a rounded wealth of information is the best way to go, and all I can hope to do is make sure my future children are well-prepared to handle the decision.