Yeah, but during that time, the teen years were more borderline adult years. Now, sociologically speaking, teen years are associated more closely with childhood and it's not until people are in their 20's that they get the chance to be considered adults.
Typically, the religious views behind pro-life also push for "no sex until marriage" and this doesn't obviously isn't the case.

Yes, some kids have sex no matter what, but IMHO, this is also the result of a too busy, overachiever mama who doesn't have time to connect with her teenage daughter issue. I'm not even gonna mention the need that the baby has for his mother, especially with DS and she's obviously so busy that her position takes her away from her child at 5 days.
I'm not either pro-life or pro-choice, as I see both sides. If Roe vs. Wade had been a year earlier, there would be no OrganicMama, but I do not agree with the extreme viewpoints of the pro-life side. The issue lies much earlier and deeper than that, something that I don't think the religious right wants to deal with, like openly teaching our children (especially daughters) about respecting their bodies and about simple biology. Teenage sex will still happen, but at least the informed knowedge & choice is there.
Feeling bad for Bristol and the rest of Palin's kids right now. An uninvolved, extra busy mother leaves plenty of room for things like this.