I think this is compounded by the fact that many of the social institutions that used to exist are also greatly reduced, and children are expected to be much more structured now than they were. Used to be that kids could reasonably be expected to walk to a library or playground on their own, or play with neighborhood children, without being constantly supervised. (And yes, bullying happened, and yes, so did the Atlanta Child Murders. But the former was a much more realistic problem than the latter.) Kids were also going with parents to church, parents probably had some kind of social outlet, etc. There was, in general, more community. (I'm not bemoaning the loss of religion, since I think religion is trash, but I do miss the community that religion helped build.)

And yeah, most people I know now that home school kids are doing it to ensure that their kids aren't exposed to 'dangerous' ideas.