I think it is a case of where you draw the line in terms of "pushing too hard." goodbye. Some parents draw the line too indulgently imho. A lot of things in life that are truly satisfying take consistent effort. (Music, sport, mastery of a new skill, etc.)
I know capable children who's parents fret that they are falling behind and are not likely to reach their potential. I'd never be rude enough to point it out directly, but allowing kids to lie on the couch for hours staring at a screen and eating junk food is probably part of the problem.
My perspective may be skewed. I live in an area where a lot of families can afford private school, but don't choose to. I don't actually know any who choose state school as a matter of political principle. I do know many who would consider paying for education a waste because the money could be sent on so many other pleasurable consumptions. They understand themselves as passive consumers; not doers. People with this mindset don't get up early on the weekend with their DC to go museums, mountain biking, drive for miles to get to tournaments, etc. They lounge around; their kids lounge around. Then they get annoyed when their kids get left behind.
I don't expect my children to be born as confident, self starters with no input or effort from me. My DH and I both encourage them, do things with them, and insist that they carry through on commitments, even when it's cold, rainy, or they just aren't in the mood.
In my little patch of London, it's not private or state school that really makes the difference and separates children, but instead parental attitudes. Too many duvet-days, passive entertainments, and junky treats doesn't build resilient, confident, healthy adults. (Note: I said too many, rather than any at all!)