even if you're correct about the cost of imposing reasonable egalitarianism being too high in any given situation

I didn't say this. Actually, I'd consider it somewhat incoherent in the context of my argument: if imposing reasonable egalitarianism (whatever "reasonable" is) was too costly to be sustainable, it seems unlikely that we'd have developed intuitions calling for it.

On the other hand, I suppose one possible scenario where that'd make sense would be if some of the emotional architecture driving our sense of equity evolved in the context of band-level societies, and if that architecture turned out to scale poorly -- but that's rather speculative, somewhat at odds with my sense of history, and in any case irrelevant to the point I was trying to make in the grandparent.

Anyway, don't read too much into it. My point was about the relationship between the world and its mathematics and our anthropomorphic intuitions; I wasn't trying to make any sweeping generalizations about our behavior towards each other, except in the rather limited context of game theory and its various cultural consequences. I certainly wasn't trying to make any prescriptive statements about how charitable we should be.