The payment would be just a one-time thing (at least in the article's sense), right? It's "only" $.99, and I'm sure it would indeed help cut down on some of the nasty responses. But I like being anonymous (even when I don't have anything nasty to say, lol). Like PP said, it's too scary to think that people can look me up otherwise.
Another thing to think about: what about the folks that don't have credit cards? Are they not allowed to leave posts, since they have no way of verifying their identity? It would affect some lower income people, yes (and I'm sure there'd be an argument that if they can afford a computer, then can afford at least a debit card, but they could be using the library's computer), but also a lot of Dave Ramsey (and similar) followers who don't like using credit cards. Seems a little too discriminatory to fly, especially since what happens when they start slowly raising the rate? Who's the voice of the commentaters then?