School isn't just about learning subjects. Its about learning about your society, how to interact with other people in the country you live in. Every single kid I've met who has been homeschooled has been weird. They've all been completely socially inept. They don't know how to interact properly and whilst they may be very clever in the subjects they've been learning, are completely oblivious about the majority of things going on around them at the time. Whilst these parents think they're protecting their kids, they're actually in my opinion harming them irreversibly. They'll eventually leave mothers bosom and go into a world completely unequipped to deal with the society they live in and it'll cause them real problems and hold them back.
Supplementing schooling with home schooling is great. Completely replacing it if you're the kind of parent who doesn't let your kid out to play with the other kids on the street is doing them massive harm.