Paul Graham tries to explain paternalism: 

Parents know they’ve concealed the facts about sex, and many at some point sit their kids down and explain more. But few tell their kids about the differences between the real world and the cocoon they grew up in. Combine this with the confidence parents try to instill in their kids, and every year you get a new crop of 18 year olds who think they know how to run the world.

Don’t all 18 year olds think they know how to run the world? Actually this seems to be a recent innovation, no more than about 100 years old. In preindustrial times teenage kids were junior members of the adult world and comparatively well aware of their shortcomings. They could see they weren’t as strong or skillful as the village smith. In past times people lied to kids about some things more than we do now, but the lies implicit in an artificial, protected environment are a recent invention. Like a lot of new inventions, the rich got this first. Children of kings and great magnates were the first to grow up out of touch with the world. Suburbia means half the population can live like kings in that respect.  …

One thing adults conceal about sex they also conceal about drugs: that it can cause great pleasure. That’s what makes sex and drugs so dangerous. The desire for them can cloud one’s judgement … Older societies told kids they had bad judgement, but modern parents want their children to be confident. This may well be a better plan than the old one of putting them in their place, but it has the side effect that after having implicitly lied to kids about how good their judgement is, we then have to lie again about all the things they might get into trouble with if they believed us.

If parents told their kids the truth about sex and drugs, it would be: the reason you should avoid these things is that you have lousy judgement. People with twice your experience still get burned by them.

Paul also suggests that innocence promotes learning:

Innocence is also open-mindedness. We want kids to be innocent so they can continue to learn. Paradoxical as it sounds, there are some kinds of knowledge that get in the way of other kinds of knowledge. If you’re going to learn that the world is a brutal place full of people trying to take advantage of one another, you’re better off learning it last. Otherwise you won’t bother learning much more.

Very smart adults often seem unusually innocent, and I don’t think this is a coincidence. I think they’ve deliberately avoided learning about certain things. Certainly I do. I used to think I wanted to know everything. Now I know I don’t.

This has some intuitive appeal, but it is puzzling – why exactly would learning that the world is a brutal place make one less interesting in learning more about that world?  Wouldn’t learning help one to avoid brutality?