Charity is just not a good metaphor for how liberals think about this stuff. Charity is good for the giver and, generally, good for the receiver. But it's not what you build your society upon. It's not reliable, or predictable, or particularly targetable. Indeed, very little philanthropy actually goes into the areas that social policy focuses on. And that's because it's not supposed to. Charity, rather often, is a way to demonstrate virtue or compassion. Social policy, at least in theory, is a way to try and fix a structural problem. The two cannot be swapped in for each other.
He opens the piece with the observation that many seem to have the idea that taxes, especially transfer payments, are nothing more than charity. I know I have been hearing this since the early 1980's (and I am sure this kind of nonsense was around long before). It is difficult to discuss the issue of taxes who believe that taxation is theft of personal property. It is difficult to discuss this issue with people who believe that this theft abets the subsidizing of anti-social behavior, or feeds the pathologies of the undeserving poor.
That's why I think we should just ignore those people. And read more Ezra Klein.