I'm pretty sure Megan's just being snotty here when she says that "[liberals have] internalized the notion that advocating taxing other people in order to give their money to someone else is somehow morally akin to charity." That said, I often run into conservative who believe some variant of "government programs=charity, so let's just do charity," so it's worth addressing.
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.
If I thought leaving all this up to rich people would work, I'd do that. It doesn't. But liberals view government instrumentally -- unlike conservatives or libertarians, its size, in the abstract, is of no particular interest. The choice of tool isn't a question of morality. Conservatives who think social policy is just an inefficient way to get the warm n' fuzzies they remember from that 1997 donation to LiveAid are shedding much light as to how they think about charity, but not much as to how liberals think about social policy.
