The argument on offer here is an argument for preemptive redistribution. We have to redistribute so that injustice doesn’t occur. But this kind of argument, like arguments for preemptive war, face a high bar. You need to be pretty convincing that in the absence of preemptive action, something bad will occur. I think egalitarians almost never get over that bar.
Um, no. The way you justify taking preemptive action to avoid any problem is by evaluating the likelihood of realizing various costs and benefits. You don't go to the dentist only when you can make a "pretty convincing" argument that you will get a cavity if you don't. You should go to the dentist because you can make a pretty convincing argument that doing so is likely to help you avoid and/or stay on top of cavities. This is true even though going to the dentist is likely to impose very real costs on you now.
I don't mean to be nit-picky about this, but Wilkinson's rhetorical slight-of-hand, here, serves mostly to make the "bar" for preemptive redistribution seem bizarrely high. In reality, by any reasonable standard, the bar for preemptive redistribution is much, much lower than it is for preemptive war, mostly because the likely costs of preemptive war are much, much greater than the likely costs of preemptive redistribution.
P.S. - As an additional note, I'd point out that once you get past various naïve conceptions of property rights, the bar for justifying preemptive redistribution becomes lower still. The analogy with preemptive war obscures far more than it illuminates.
Update - Will says I'm neglecting the main point of his post (viz., that there doesn't seem to be much evidence that, in general, a high level of inequality "in fact increases the chance of exploitation or unfair procedures" by the relatively wealthy). Which is true! (Was I obligated to? Maybe I don't understand all of my bloggerly obligations.)
So to be fair, I don't have much to say on that question, although it strikes me as the kind of thing that's best looked at on a case-by-case basis.
But the portion of his argument that I quoted is either relevant or it's not, and the main point of my post was that the preemptive war analogy is really not that helpful of a way, in practice, to look at preemptive wealth distribution, or wealth redistribution generally, for that matter. I think it mostly serves as a rhetorical device to make the justificatory bar seem higher than it really is. (Which isn't to say there isn't a bar at all.)