It seems pretty clear that our economic goal is to have economic abundance, where everyone can have as much ordinary stuff as they want; by definition, we would then have strict equality of income. We do not, of course, presently actually have economic abundance, so at best this form of strict equality lies in the future. What of today, then? First, does the present level of economic inequality per se help or hinder progress towards a goal of abundance? Second, should we address economic problems other than inequality, perhaps using inequality as a diagnostic or measure of success, or should we address economic inequality directly?
We do not have a world of abundance, but we do presently have (or are very close to) a world of "plenty": a world where everyone can have enough to avoid the most obvious kinds of physical and social suffering, such as malnutrition or starvation, homelessness, treatable death and disease, undereducation, and barriers to ordinary civic participation. Moreover, everyone can have the "necessities," and we will still have enough social surplus to continue expanding the forces of production. We know we presently have a world of plenty simply because all economic crises of modern capitalism are crises of overproduction. Overproduction is possible only in a world of plenty.* Given that we do in fact have plenty, we have to talk about the morality and practicality of how we distribute it.
*If you don't buy this claim, let me know, and I'll write about it elsewhere.
Because we do have enough that no one has to materially suffer, then it is a moral evil to allow anyone to suffer from material deprivation. This position is not a matter of argument: either we have this moral opinion or we don't. I'm going to proceed under the assumption that we do. (It's notable that people who seem to hold the alternative moral opinion seem to hide that opinion.) If we are going to both ensure that everyone has these necessities and account for people's consumption, then regardless of any other considerations, we must ensure that everyone has sufficient income to afford the necessities. We can, of course, do other things — e.g. improve education, equalize access to capital, ensure appropriate political and economic socialization — but we must also simply ensure that people have enough income to buy what they need. Criminality is beyond the scope of this post and topic, but we already at least pretend to offer even the worst criminals these basic necessities; how can we refuse them to law-abiding citizens? Clearly, to the extent that we share this moral vision, we must address income inequality directly.
Of course, setting a floor on income is not strict income equality. However, the need for an income floor requires that income inequality become an issue we need to address directly, neither irrelevant nor merely diagnostic. Sometimes we need to stick the camel's nose in the tent: if we accept an income floor, it becomes more politically feasible to continue to equalize income and wealth. Opponents might, seize normalization of strict equality as an argument against an income floor. But this argument presupposes the absolute good of income inequality, a presupposition that I do not think can be justified. The goal of strict equality is not some Procrustean bed of drab sameness; the goal is a society of material abundance. To be against strict equality in principle is to be against material abundance.