MaizieD
You're all still ignoring the funding factor. State schools will never become universally 'good' unless they are given the funding, and so are the services which support children and families.
But the other factor that few have touched on, is the social aspect of keeping these children in a bubble of the wealthy and privileged. They should be getting an idea of how the less wealthy and privileged live. They should be mixing with children who don't have all their advantages and they should be doing this at an age where children are far more accepting of 'differences' than they are when they hit secondary school. A few years in a state primary wouldn't do them any harm and enable them to see a rather less sanitised world than the one they usually do.
I think the extremes of political thinking do ignore the practicalities, sadly. After all, you are, at the very extremes, on the edge of revolution. Isn't that what we have had over the last decade plus? I would love the Finnish view of "education for all" to be ours. But you do have to pay for it. Can you imagine (I daren't) what it would cost to bring our schools up to that standard after the last 12 years?
The "bubble" is what some choose. I don't think you can instruct those with that view to do what you believe is the right thing for their children. Those who like school "bubbles", gated communities, etc., will continue to do so. Again, it is how you persuade them to change. A proper tax system would help, of course, but I am not sure telling them that it wouldn't do their children any harm is going to work.