Well he's right, but in the most pointless way you can be right. Knowing that heroin exist doesn't make you an addict, and there is an argument to be made that if you know about it and you know the dangers you're better at avoiding it. Rather than learning about it from people your age that don't know anything about life.

That said i don't remember sex of any kind being taught in school. You don't have to learn it. It's innate.