To add to your points, a very important consideration is that charter schools can game the metrics by forcing out students who aren't performing well, while public schools can't turn anyone away. This may be why they seem to improve test scores without making any actual difference [1].

Public schools can use charters to game metrics themselves too [2].

[1] http://www.nber.org/papers/w22502

[2] https://www.propublica.org/article/alternative-education-usi...

I don't think the argument is tautological because right now, the public controls the cost of education and how that cost is allocated by our votes for taxes and bonding and by elections of local school boards. If we opt to increase or decrease that funding, it is based on the assumption that the funding will provide a certain level of education and that we can also elect people that oversee that education. Once you bring private schools into the mix, questions about cost become much more complicated. Can a private school charge tuition beyond the voucher amount? If not, what the point of it being private, isn't it just a public school in everything but public oversight? Right now, if I reject or approve a bonding referendum or vote for a school board member, I am offering my opinion on how a school system is run because my vote has a direct effect on how much money goes to the schools and who oversees that money. But if it goes to vouchers, do I lose that control?

So no, I don't think the depletion argument is tautological because we do not have citizen control over how a private school is run, by definition. If they opt to charge more for tuition that the voucher covers, the depletion argument is very real, because people with more money can provide a better education with public subsidies. Even if they cannot do that, we still do not have oversight of those funds.

Disagree but your post is another wonderful example of civil debate. Thank you.