I've written this in an earlier entry but I seem to be using it often these days.
Homeschooling families (most of them) do NOT want their kids sheltered in a greenhouse. They want the sun to shine on their heads, the rain on their faces, the wind in their hair. They just want to be able to choose what grows up next to them.
The world would weigh us with knowledge of things for which we have no strength to bear at such an early age. The ability to carry that knowledge will come in due time, but there isn't any need to burden a child with adult ideas and actions too early. The world's purpose in burdening a child is to break that child, and form the child to the whims of the world. A set of loving parents can choose a more appropriate time for a child to take on the world.