In the meantime let me respond to a few of your other comments.
Jeremy - I am talking about native, i.e. innate, wit, intelligence and drive. On the (possibly false) assumption that this is distributed fairly evenly across social classes, then we clearly don't have anything approaching a meritocracy (given "merit" is based on the abilities etc. that the education process starts with, rather than finishes with).
This is one of the ambiguities of talk of a "meritocracy". Seems to me it would be odd to describe as a "meritocracy" a system in which native talent etc. is distributed fairly evenly across social classes, but, because the top seven percent pay for a far "superior" education, their children end up far better educated (and/or far more confident, far better connected, far-more "posh"sounding, etc.) and as a result dominate the high-status, high-earning professions. Certainly, however you describe it, it seems to me that such a system (i) involves a great waste of native talent, and (ii) involves very considerable injustice.
Potentilla - yes - the "right to educate your child privately" objection. Well, consider an analogy. Suppose that Oxford and Cambridge decided to drop selection on the basis of academic ability (other than to a reasonable minimum standard) and select instead on the basis of cash. Their fees go through the roof, with the result that only 7% of parents can afford them. Other universities find their funds dwindling, their best staff fleeing to now-loaded Oxbridge. With their vastly superior funding, Oxford and Cambridge produce highly-polished graduates who then out-compete others for jobs, with the results that they dominate the high-status, high-earning professions.
What would be the public's attititude to this? Many, I think, would consider this a shameful situation. The majority of the nation's native talent would be wasted. There would also be great resentment and frustration, and a sense of a country divided. There is a very good case, I think, for preventing such a situation arising. Of course, this would involve denying rich parents the right to buy their children a superior university education, and, thereby, a ticket to the front of the good-jobs queue. To which the response of many would be "tough". And rightly so, I think.
Some of you may think this is a bad analogy. Others may think that such an outcome (Oxbridge becoming like a private school) would be no-bad thing....
Georges - I'm making no assumptions about the motives of each and every parent that send their kid to a private school. I am only concerned with the outcome of their doing so, and the justice of their being able to do so. I am just exploring those two questions.
Some other points:
I am not assuming a private education is educationally superior (or I don't have to, anyway). Merely that it provides a very major advantage to kids in terms of their life-chances. It may do this in other ways (i.e. not being being educationally better, but by making them sound posh and confident, making them better-connected, etc.)
I notice, by the way, that some objectors say private schools don't provide a much better education, which is a reason for not banning them, whereas others say they really do provide a better education, which is reason for not banning them.
BTW, I am not necessarily objecting to selection. When Grammar Schools were introduced (selective, non-fee-paying) a lot of working class kids suddenly found their way into university and beyond. Perhaps that's the way to go....
Barefoot Bum: Yes, the rich will find other ways to give their kids an advantage. And yes, Jacob, the kids of the upper middle-classes have other advantages too. A few will be able to afford to send their kids abroad. That doesn't mean it's not a good idea to take this particular mechanism away from upper-middle-class parents (if it is particularly unfair). After all, ensuring there's no racial discrimination in the workplace won't prevent racism manifesting itself in other ways. And fitting window locks is a good idea, despite the fact that burglars will in some cases find another way in.
I think Joe Otten's point is a good one. Native talent is just as undeserved as privately-nurtured talent. In both cases, it's the luck of the draw. I may find myself having to defend redistribution of wealth and other rewards towards the congenitally thick.
Lastly, the suggestion that without private schools we may never get that one wonderful scientist who will cure cancer - I don't buy that. First, on the assumption that native talent is fairly evenly distributed across the social classes, given that only 7% of it receives a superior private education, and thus gets a vastly improved shot at getting into Oxford to study medicine, etc. then, as a result of private schools, we are currently missing out on much of the non-privately-educated 93% of innate, genius-level talent that's out there. Secondly, ban private schools and, yes, I admit you will probably end up with some drop in the quality of education received by those applying to Oxford. But you will now be able to select for native talent far more effectively. You'll be accepting far fewer highly-polished second-raters, and replacing them with rough diamonds. So, I suggest, the outcome at the end of university education will be much improved - many more polished diamonds, as opposed to lots of even-more-highly-polished second-raters (note that, even now, state-school pupils outperform their privately educated peers at Oxford - why? because they have more native talent.).
Remember it is the education they receive at University that turns children into doctors, researchers into a cure for cancer, etc. As long as schools are able to bring kids up to a reasonable standard, I think the gains made by having more of those with native wit and ability studying medicine and science at Oxford will more than compensate for the fact that none of them had the earlier educational advantage of going to Eton. We will have more genius-level talent working on a cure for cancer.
Also remember, as I said earlier, I would be equally happy with all schools privatized with a voucher system in place but No Top Ups (everyone has the same amount to spend). So the point about the inability of the state to deliver quality education, etc. is simply not an objection.