Traditionally, public schools have enjoyed a monopoly over public education. A monopoly power does not fear competition, and so is not motivated to improve because all of the customers in the monopolists market have no choice but to buy the monopolist's service. Charter schools inject much needed competition for education dollars, which should spur positive change in the public education market.
When parents are given charter vouchers for schools, the less favorable schools suffer. All of the children in the most impoverished areas remain in the worst schools. All schools need to be fixed from the ground up; it should not be left to individual schools to pull themselves up by their boot straps when they simply cannot.