I stuck by my pledge. And I know of plenty of others who suck by theirs.
Which is more "foolhardy": to teach a high standard, knowing that some or even many will not follow it, or to teach a low standard and then act surprised when kids start following it?
What standard you teach defines what you are telling kids is acceptable. If you teach them abstinence-only, then they will grow up with the mindset that abstinence is the only thing that's acceptable (not a bad standard even for a non-Christian). If you teach them that "abstinence is best, but if you're gonna do it, here's how", then you are teaching them that premarital sex is ok, regardless of what you think you are teaching them.