What boots that? That the marginal value of the money is less from the rich's point of view is a practical matter, not a particularly moral one. That is, unless you ascribe to the notion of "From each according to his ability, to each according to his need", as admittedly many people do, I don't see any intrinsic reason why one person should owe the state 1000+ x per year what another one might, other than the fact that they have it to hand over.