You misunderstand how charter schools work. The students pay no tuition. They are public schools, government regulated, but operated for the benefit of the students and parents who want to opt out of the local public school. Funding accompanies the student in an amount at or below (depending on the state) the amount of per capita expense that student would have had at the public school. In other words, the charter school takes the same amount of money (or less) and does a better job with it.
It can do a better job because it is not saddled with the union work rules, salaries, benefits, etc. and silly rules that the public schools have. Their educational results are better, which explains the many people clamoring to get into charter schools.
Opposition to charter (and voucher) schools comes mainly from the powerful teachers unions, who do not want to see their government-enforced monopoly threatened. They are naturally embarrassed by the educational results of charter vs. public schools, especially for minority and poorer students.
