For one thing, we project the merit of parents (or lack thereof) onto their children. We do this in how we allow massive intergenerational transfers of wealth. But also, as you point out, the schools a child can attend are very dependent on who their parents are.
In Chris Hayes' excellent book, Twilight of the Elites , he rejects meritocracy. Not only does he reject it in practice, for reasons like those I presented, but he also rejects it even in theory. He suggests that the idea of showering people with resources that show promise is an affront to the concept that every human being has fundamental value and that all should be invested in.
Liberals, broadly speaking, do love schools. But I don't think that's for lack of concern about other issues of social justice! Perhaps you mean economic liberals (e.g. classical liberals and neoliberals)?
The short summary on amazon is pretty good:
Over the past decade, Americans watched in bafflement and rage as one
institution after another—from Wall Street to Congress, the Catholic Church
to Major League Baseball—imploded under the weight of corruption and
incompetence. In the wake of the Fail Decade, the social contract between
ordinary citizens and elites lies in tatters.
I wish I could upvote this so many more times.
It honestly had never occurred to me that meritocracy could be a bad thing until I read Twilight of the Elites by Chris Hayes (yep, the same MSNBC host guy) , recommended to me by a friend. But after reading that book, which is one of the best written and edited books on econ/policy I've ever read, I'm fairly well convinced. He builds very much upon Michael Young's work, which he mentions many times, applying it to all sorts of examples of meritocratic failure in the modern day.