But I don’t believe a single person who tries to justify it by saying it saves money for state schools because they do so.
I've seen this attempted gotcha a few times, and I find it really strange.
No one is saying that to 'justify' our schooling choice. We're pointing out that it's a consequence. Which it is. We're pointing out that our choice saves you money, and us changing our choice will cost you.
Using 'that's not why they do it' as a supposed gotcha shows a fundamentally different value system to mine. Do you really think the actual consequences matter less than the whether the motivation is pure?
To me, motivation matters a bit (mainly because it predicts future choices) but real-life consequences matter much, much more.
I don't really care whether Billy Burglar has given up his life of crime due to a new-found respect for other people (unlikely) or whether he doesn't want to go back to jail.
I just don't want him to burgle my house.
I don't care whether you've chosen to work as a plumber instead of having a life on benefits because you want to contribute to society (unlikely) or whether it's because you calculate you can live in a nicer house and go on holidays.
I just want my taxes to be lower due to having more financially contributing members of society, and I want to be able to get my shower fixed.
I don't care whether someone is sending their kids to private school because they want to save the state money (unlikely) or whether it's because they want their kid to have a great education and a happy life.
I just want my taxes to be lower because I don't have to pay for their kids education or travel costs to an out-of-county school, and I want to get a pension in 20 years time because more kids are successful, and contributing to society instead of long-term sick with anxiety