I agree that it should up to the parents, but I also think sexual health is an important part of an overall health curriculum.
I'm a product of an abstinence-only education, and let me tell you, it wasn't just limited to "no sex is the safest sex of all." After showing us slides of genital warts, my gym teacher held up a heart made of construction paper. She ripped three or four pieces from it, then pointed to the torn-up stump and said, "Every time you have sex with someone, you give him a piece of your heart. When you get married, this is all you have left for your husband."
My parents never had the talk with me (I don't know why), but if they had, I might have been less influenced by such "lessons." While I think it's important to teach teenagers to protect their hearts and choose their partners wisely, there are much better ways of communicating this. And, as you can imagine, there was no instructional time devoted to birth control, condoms, responsible sex, etc.