Pragmatists say we're better off accepting that children and teens will do the things we warn against anyway, so a better, safer route is to manage the outcomes to the degree we're able - supply condoms, collect the car keys and host the kegger at home and legalize marijuana to avoid the potential for a criminal record.
Still, most everyone agrees that high-risk behaviors like these are not good, not healthy, not desired. Abstaining may be tough, but it's still the best solution.
Miss Palin may think her parents' advice regarding abstinence was unrealistic, but I think that was the 18-year-old daughter talking.
The 18-year-old mother will soon discover that unrealistic expectations drive the parenting bus.
With time and experience, perhaps she'll discover that we parents have another name for those unrealistic expectations. We call them "ideals."
Without them, parenting would be near impossible.