Even as an entirely utilitarian classical liberal it's possible to, in theory, be worried about economic inequality. If a society is so unequal that we don't have, nor cannot have, equality of opportunity then this isn't a society that's living up to the liberal ideals. We might therefore want to do something about said inequality. For example, imagine a society in which large swathes of the population are inadequately fed in childhood, leading to stunting and possibly a diminution of their IQ, meaning that they're most unlikely to pass by their richer and better fed contemporaries. This is of course what has been true across vast swathes of the world throughout time and is still true in the poorer places. We would therefore argue that something must be done in order to improve matters: which is what we do do, it's imperative that those poor areas be able to experience economic growth sa a result of some judicious dollops of capitalism and free markets.
But imagine that this was still true in a rich society: like, say, the UK of today. In fact, that's what part of the argument from our current left actually is: that the poor of our society are not able to deploy their God given gifts as a result of the poverty in which they grow up.
But is this allegation true?
Research suggests that genes and environment both play a critical role in shaping a person's intelligence. A longstanding hypothesis in the field of behavioral genetics holds that our potential intelligence, as set by our genes, is more fully expressed in environments that are supportive and nurturing, but is suppressed in conditions of poverty and disadvantages. While some studies have provided evidence supporting this hypothesis, others have not.
A reasonable statement of the question at issue. The answer?
The researchers found that the relationship between genes, socioeconomic status, and intelligence depended on which country the participants were from.
"The hypothesis that the genetic influence on intelligence depends on socioeconomic status was not supported in studies outside of the US," says Tucker-Drob. "In the Netherlands, there was even evidence suggestive of the opposite effect."
Importantly, the meta-analysis did not show any evidence that other factors -- such as age of testing, whether the tests measured achievement and knowledge or intelligence, whether the tests were of a single ability or a composite cognitive measures -- influenced the results.
That is, UK levels of inequality don't matter. We've got that basic floor to the welfare system that allows full human flourishing of those given gifts and that's all we need to do.
Given that equality of opportunity is the aim and that's what we've achieved in terms of basic living standards (although obviously, not necessarily so in terms of access to decent education and so on) then on that issue we're done. We just don't need to collapse economic inequality any more than we already do.