I don't think £50k, £80k, or £150 is the norm. Median is £35k or something similar. But that's not relevant.
What's relevant is the economics. And that hinges on the choices of people earning (in the example I've suggested) £100-150k, on marginal tax rates of 62 and 47 per cent.
Those are different choices to those available to somebody else already on £50k or £80k or less; different choices to those of single mums, cancer victims, the recently bereaved or domestically abused, people in Gaza, etc etc. I'm not belittling the various challenges facing any of those people, they just have no bearing on the purely economic problem of "will this education tax raise money and sufficiently so to justify the costs/harms it causes?"
I agree the actual outcomes are hard to predict. Maybe everyone just sucks it up. Maybe more schools close than anyone expects and you get 20k redundant teachers and 100k kids migrating for a loss of £1-2bn and total chaos in state schools. Nobody knows - but economically, the benefits are at best small, and the risks are very large. It's a stupid policy and a colossal distraction from improving state schools.
And I don't think anyone with intelligence and integrity should tolerate crapping on a minority, rich or poor, just because "it's popular" and "there are other causes worth defending". They'll be coming with pitchforks for something you care about next.
If you're so much a high earner, and you're ambivalent about what some would call the "privilege" of private school that you've been able to buy for your kids, will you be paying for the back VAT you were lucky not to pay? Sounds as though you have spare money.