The thing is, two of the most important books on this subject in recent years - Roemer’s Theories of Distributive Justice and Kolm’s Modern Theories of Justice - almost entirely neglect the notions of desert or merit.
There are, I think, two reasons for this.
One is that it’s impossible to tell what any individual really deserves. Do I, for example, deserve to earn more than the average worker? In one sense, no: my work is much less onerous or unpleasant than the average. But on the other hand, this pleasant outcome could be a just reward for years of effort earlier.
I don’t know which it is - or at least, I don‘t if I slough off the self-serving bias! - so I’m blowed if I can judge anyone else’s income. For this reason, I share the Devil’s consternation at the idea that public opinion should adjudicate.
Secondly, it’s possible that none of us deserve anything. This isn’t just the traditional Christian position that we are all miserable sinners. It’s also the Rawlsian one, that the distribution of talents - which include an appetite for hard work - is “arbitrary from a moral point of view.” And of course, none of us “deserves” the enormous good fortune of having been born into a liberal democracy in the late 20th century.
For me, these reasons suffice to disregard “desert” as a macro principle colouring our views about the distribution of income - though we might use it in other contexts, as when we say “he deserved that goal” or “he deserves to go to prison for that.”
This is not, in itself, a particularly leftist position. Intelligent libertarians share it. Hayek was wary of the idea of desert, and Nozick wrote of entitlements, not desert; there’s a difference.
All this said, I share Sunny’s view that there are distinctions within the “rich”. There is a difference between the talented footballer or musician or the innovative entrepreneur on the one hand and the rent-seeking exploiter on the other. But our tax system doesn’t - and probably cannot - make such distinctions. Which is, perhaps, one reason why the state alone cannot achieve social justice.