With respect to cost, I'm not sure any of these points refute the hypothesis that charters cost less per pupil primarily because they are able to offload the most expensive students. And if that is true then increasing the number of charter schools will simply increase the concentration of the most expensive students into fewer schools that have less funding to deal with them. At that point we can either acknowledge that expensive students require an order of magnitude more money or we let them pass through to the welfare and justice systems. In either case it doesn't seem like we're saving society money by switching to charters, we're just shifting it to other parts of the budget.

With respect to educational opportunities that seems more compelling. But as Sowell alludes, I suspect you could get a similar effect by allowing public schools to enforce stronger discipline and make it easier to suspend or expel difficult students. On that note I'm surprised to hear that teachers unions are opposed to that now. I've certainly heard that unions are an obstacle to getting rid of poor-performing teachers, but I rarely hear of them being an obstacle to dealing with difficult students. At least a couple decades ago the AFT was actively pushing to make it easier to expel students for things like drugs or weapons in school.