tbh, I think debates like this would be a lot more productive if everybody stopped calling other people hypocrites, or accused them of having a chip on their shoulder etc.
Thing is, most people want to do what is best for their DCs. (I do know parents who don't give a stuff what school their kids go to but let's disregard them for a moment.) And we all make that choice in the context of what exists. So you might have personal objections to grammar schools, but if you live in an area where there's still a grammar school system, you'd probably want your kid to go to the grammar school rather than not.
People who think that private schools give richer families an unfair advantage over everyone else still probably don't want to send their kids to a really shitty comp, so they compromise by moving near to a good comp. You would, after all, be a pretty odd person if you deliberately sent your child to a terrible school.
Of course Takver is absolutely right to say "once enough people opt out of the catchment school for a 'better future' for their dc, then the catchment school gets a critical mass of social problems etc etc, and more and more people feel obliged to opt out because they fear their dc ending up at the bottom of the heap in a highly unequal society."
The trouble is, you can't account for how everyone else will act. Yes, it would be brilliant if all the naice middle class people sent their kids to the local comp so that the local comp improved. But you have to make your choice as an individual, and no-one is going to want to sacrifice their child's education to the greater good. Unless people agree to act collectively (which they won't do), you're left making difficult individual choices.
So the solution to uneven quality of schooling lies with government, not with individuals.