IMHO it's a distraction to discuss whether or not wealthy people should send their children to state schools. All children are entitled to a state education, aren't they?
My interest is in whether this policy is a net good or not.
For example:
Will some children be adversely affected? I would say yes, e.g. if their education is disrupted by their private school closing or being removed particularly at important educational stages, or if children who would have got a place at a particular state school are displaced by children moving from private. So then the question is, does it matter in the grand scheme of society for X number of children to be affected? Policy supporters would presumably say no it doesn't because it'll be a tiny percentage.
Will state schools benefit from the arrival of the engaged, sharp-elbowed, supportive families with clever high-achieving children who have been siphoned off by the private sector? Policy supporters would presumably say yes, there will be raised standards, improved behaviour and a flowering of parental donations and assistance, because if not (see tiny insignificant percentage thing above) then what would be the point for the grand scheme of society?
Will it cost some state schools more in money and resources if the arrivals from private are children who have SEN, having previously been failed by the state sector? Will it exacerbate the behavioural issues and disruptions highlighted in earlier posts, which have got worse since COVID? Policy supporters would presumably say no, because it'll be a tiny percentage of the overall numbers/cost.
And ultimately, will there be a net amount of tax raised by this policy? There was a government report saying that it would raise £WhatEvs, which IMO seemed to be based on assumptions such as only a tiny percentage of children would move, and that in general families using private schools are uniquely not incentivised to change other behaviours in the face of financial pressures. IIRC the report itself acknowledged that above a certain percentage of movement, the policy would lose money.
So the question is, will there be a tiny percentage moving/being affected (resulting in net £££ for 6500 teachers housing, plus no significant increase in SEN resourcing costs etc) or will there be sufficient number moving (resulting in glorious uplift of the grateful state school recipients of the clever, engaged movers)?
I think the honest answer is: Nobody knows.
And the next honest answer is: It doesn't matter in the end what the net result is, because nobody will ever accept anybody else's data collection, so people will delightedly applaud (if supporting) or just have to suck it up (if against).