Many parents are not comfortable talking to their children about this sort of thing, or are not familiar with it enough themselves. None of the people I grew up with, or any parents I have interacted with, ever brought this up with their kids or were taught about it themselves. In rural, conservative areas like mine, this is a taboo topic, people are silent - and my state has the highest rape rates in the nation. Talking about abstinence isn't going to make teens go "gee golly whiz mom, you're right!" Even if they remain abstinent, this is knowledge people need to know. I see people arguing against this saying the education system is inadequate - then why can't we start trying to fix it?