In a comment on my previous post, Luis Enrique asks why I am opposed to small moves towards equal opportunity. As luck would have it, some new research shows a reason.
Kai Konrad and Florian Morath ran some laboratory experiments, in which subjects were assigned wages and then asked to choose tax rates. They found that where there was no wage mobility, the chosen tax rates were pretty much what you‘d expect; the low-paid vote for high taxes and the high-paid for low taxes.
They then introduced random social mobility. They found that this significantly reduced preferred tax rates. People on low and median wages chose lower taxes, in the hope of getting higher wages later. This more than offset the (small) tendency for the well-paid to prefer higher taxes.
What worries me here is that this might not be entirely rational. Some combination of optimism bias and the just world illusion might cause people on average and below-average incomes to exaggerate their chances of becoming well-off, and so lead them to favour lower taxes than their objective prospects would warrant.
Efforts to increase social mobility - which are of course likely to result in only minuscule actual changes - could exacerbate this wishful thinking.
In this sense, egalitarians should be wary of policies to increase social mobility, because they might (irrationally) reduce public support for redistribution. In this sense, there is a trade-off between social mobility and true egalitarianism.
A thought experiment. Imagine a society which randomly imprisoned a fraction of its population. Every week, a few prisoners were selected at random for release, and a few free people randomly selected to take their place. Such a society would have social mobility and equal opportunity. It would, though, be absurd to call it fair. This, surely, shows that social mobility is not sufficient for justice, and that it can exist in very unjust societies.