I hate to be graphic, but the fear of pregnancy is leading many young people to engage in "unnatural acts", instead of normal sexual intercourse. That, and a general rise in promiscuity, is what is leading to the skyrocketing STD levels.
I know "nice college girls" that are in their early 20s and have lost count of how many guys they've had sex with, and what their first names were. There is absolutely no shame attached to this. In fact, they are celebrated and popular for this behavior.
But the real reason for the rise in unwed pregnancy (which is the real problem, not the fact that they're teenagers) is fatherlessness. It's far and away the biggest predictor of unmarried pregnancies. Not only are those girls more likely to have premarital sex, they also are more likely to: drop out of school, grow up in poverty, watch their own mothers (their role models) practice serial monogamy, never marry, abuse drugs and alcohol, start having sex earlier, have more partners, and begin menstruating earlier (and are therefore more fertile).
But you won't hear that on the news. Illegitimacy is related to marriage and nobody wants to touch that with a 10-foot pole in the dark.
Now, I'm not a big fan of the guy who originally posted this graph, but the data he used are completely correct and valid. Take a look at this and then decide if more information would have stopped these unmarried girls from having babies. These girls know more about sex and reproduction than most married women with children. You could take lessons from them. They are not pregnant out of ignorance; that's just propaganda.
Illegitimacy rates went from 5.3% of births in 1960 to almost 40% in 2009. That's an increase of over 700%, and that is after sex education began to be taught in public schools. The debate about the kind of sex education taught is a red herring. The bigger question should be: why is it necessary to teach children about sex at all.