Via Julian Sanchez, I see that Matthew Yglesias is arguing that it’s just to guarantee that Social Security benefits keep up with wages rather than prices: “As general living standards improve, so do one’s reasonable expectations of what constitutes a dignified retirement.” That seems to me to be true.

But today’s level of taxes is not capable of generating benefit levels that keep up with wages. To the extent the program is redistributive, maybe that point doesn’t matter: You could just raise taxes on the rich to fund those benefit levels. But it would not make sense to raise someone’s taxes in order to keep his own benefit levels high. Most people would, I’d guess, prefer to keep their taxes low and invest the difference rather than to pay more taxes to see their benefits rise.