The pressure argument also doesn't fly - at least, not with me.An unplanned pregnancy causes amazing angst, and it's very easy to pressure an anxious woman, especially one who has literally no one to "run as hard as you can the other way" to.
Thus, the reason that children, who don't fully understand the consequences of their actions, should not be engaging in adult behaviors. If people don't use condoms and/or other birth control methods to prevent unplanned pregnancies, despite ALL of the information that is available, whose fault is that?? It's the same thing as smokers claiming they didn't know that smoking causes cancer.