I like Ebert's writings on movies a lot. But in this case, I get the sense that old age is a factor. Or more precisely, a certain rather distinctive kind of pessimism that sometimes afflicts old people. It happened to a professor of mine that I love. And earlier this year I heard an NPR piece about the 100th birthday of Claude Lévi-Strauss that talked about how he had lost all hope for humanity. As I said, there's a kind of distinctive quality to this that makes me think it isn't really about the state of the human race... it's rather more self-centered than that (which sounds more judgmental than I'd like).
Yeah. To be fair to the poor guy, he's gone through a pretty miserable last few years. Lost his voice, disfigured his face, saw the most hated movie critic in the nation replace him at his flagship show. I'm guessing it's not easy.