Don't we all remember the isolation we felt, even when there were other children physically near us, everyday in school? Can you imagine how devastating the effect would be to have such severe social and physical isolation as one would encounter in a home schooling environment?
School is at least partially designed to offer views and exposure not available in the home. Children need the extended social interaction. They need to work things out in unfamiliar environments. They need to be out there where mommy (no matter how good a teacher she might think she is) is not there to step in for them.
I question the motives of parents that would lock up their kids in a home school. - and don't anyone fire off any trash about their kid getting out for 4H, or gym at the regular school. Parents that subject their kids to such oppression are so self-centered that they think the only useful opinion that their children should be seeing is their own. Either that, or they are so short of confidance in their children, that they think their children won't be able to handle the social side that all the other kids can.