The point of public schools is to teach acedemics, not morals. Sex ed, gun ed, etc. are outside the scope of the true mission of schools. I was fortunate that during my time in school I wasn't subjected to the non-acedemic crud.
Regarding private schools, as a deist I wouldn't send a kid to any that have a religious bent. I've got no use for religion either.
Home schooling seems to be the only way to ensure your kids get the exact education you want them to have these days.
I'd argue the purpose of school is to produce adults who are capable, at the very least, of some basic level of existing in society, and less cynically, to make kids into the the leaders, innovators, business people of their generation, ultimately, to to teach kids how to become informed citizens. Sex education (and the idea of gun education proposed here) nominally, should be about the facts surrounding these things, not about whatever some religious denomination feels the implications are.
For the longest time, there were a lot of things I was sore about my experience in public education, namely the opportunities I missed because I wasn't raised in the affluent part of town, where high-school is more like a mini-college campus, and is treated as a way to ready students for college. Visiting such a campus during advanced-placement class activity, it was a real contrast to my high school, which was probably better at readying kids to work at McDonald's or Waly-Mart. College was a real culture shock, even though I was on the honor roll, I entered that phase of life totally unprepared.
Sex education wasn't one of those things I felt bad about, though, because it was treated in a no-nonsense, no ******** manner, and even though I already knew most of the things taught in that class, it's conceivable, err...probable, that some people's families shield their kids from this knowledge the same way others shield their kids from knowledge about guns. Functioning citizens need to know 1+2=3, it's the same thing with sex ed, as far as I'm concerned.
A related, anecdote I've witnessed with my own eyes: the wife of one of my cousins was so restrictive regarding her children's toys, they were never allowed anything that shot any kind of projectile. As I was growing up, I enjoyed these sliding-piston blasters which shot 1 inch foam balls, accompanied with a loud, silly popping sound. Dad and I would stalk each other around the house and tag one another for hours on end. Best toy ever, basically.
One Christmas while I was in my teens he brought the blasters and balls to the family gathering, thinking the kids would also have a lot of fun; he was chewed out on the basis that these long pink tubes were too much like guns, and that under no uncertain terms were her kids to be exposed anything like that, ever. I later taught one of the cousins to use one of my old bow and arrow sets, after he expressed interest at a Renaissance fair, and remarkably, he continues to be enthusiastic about bows and arrows. Thing is, I see in these kids that unpreparedness I felt in myself as I was entering college, except for life in general. Oh, that mother is pretty freaking religious, too. Approaching the level of the mother in Carrie.