Lack of Imagination
One of the things I struggle with in arguing for ending the government schools monopoly is a lack of imagination. In most people's lifetimes, there has never been a robust network of private school options to fit all needs and budgets, so folks assume that that such choices can't exist -- that there is some structural failure of capitalism that would prevent these choices from existing rather than structural government factors that have prevented them from existing.
Don Boudreaux has a nice analogy that helps make the logic of school choice clearer.