Don't they teach this stuff in high school?

Yes, they do teach this stuff in high school (and middle school and elementary school for that matter), but they generally had an agenda significantly different from "give students the most accurate possible information about how to be healthy." Based on my admittedly anecdotal recollections, the main goals were to scare us as much as possible about sex and drugs and avoid having to explain anything complicated. As such, I would trust the LW community far more than what I was taught in school.

Of course, if you want to get your health advice from DARE and the Food Pyramid, I guess that's your right.