I think there are different economic mindsets:
1.That the best way to improve everyone's lives is to redistribute money fairly
2.That there isn't a fixed amount of 'value' created each year, and that the best way to improve everyone's lives is to structure things so that more value is created. That if everyone gets a bit more, but some people get lots more then that's preferable to everyone having less.
The different mindsets cause huge frustration on both sides for lots of topics, including this one.
Group 1 think that private school parents are selfish for resisting redistribution.
Group 2 think that it's stupid to make everyone poorer just so that everyone is more equal.
@Newbutoldfather - you asked How do you campaign for a better state sector when those with power and influence opt out? Why would you care if it doesn’t affect your child?
Of course I care about state education, because most of the UK's citizens are educated in state! And it's not just that my doctor and my kid's teacher were educated in state schools, it's much more than that. It's that how pleasant my city centre is in 20 years time, how much theatre and arts are available, how quickly I'll be treated at hospital, how well-stocked the shops are will depend on how productive the next generation are. Oh and the guy I meet on the street will be more or less inclined to crime depending on whether he has a job, which in turn depends on whether private companies are thriving. And it's a cycle where better education now means more money available in 20 years, which means better education in 20 years, which means... you see where it's going. We're an interdependent society: of course it affects me, regardless of where my DC is educated.
The strength of our economy isn't fixed. How much value is created depends on the ability, skill and hard work of all workers collectively. And that to quite a big degree depends on their education. Opportunity isn't zero sum: my DD being a better engineer doesn't make your DC a worse entrepreneur.
Why don't you care that some kids end up with a worse education from this policy without any real benefit?
(Oh and the reason it feels like an attack is that it's such an obviously ineffective tax in terms of UK economic benefit that when you think the group 2 way, you can't see any reason to introduce it except to cause deliberate harm)