I'm beginning to develop two uncharitable ideas about why people think homeschooling parents must have some form of qualification in order to teach their children.
1) I couldn't trust myself to do that.
2) People can't be trusted to do that.
Number one is probably the one I see most often. They don't trust their own knowledge when it's unaccompanied by a $40,000 piece of paper. They don't trust their ability to judge the knowledge of others. They don't trust that learning can happen without a teacher leading them by the hand. They often don't even seem to trust that they can learn at all once out of the environment of school.
Number two generally represents those people who don't have a problem trusting themselves. They're very sure of their own abilities and knowledge, they simply know that everyone else can't be trusted. This is because we aren't them.
One group has been molded by the system of education to think they can not function without it. The other group has become the system.