There's a good argument that he was in the 1990s. That doesn't mean he is one now. People change.
But let's suppose for a moment that he was one, and he hasn't changed, and he still is a terrible person underneath. Does that make the people who would have got malaria but didn't because of the Gates Foundation's efforts any sicker?
Or, contrariwise, consider some area where it turns out that the work of the Gates Foundation has done harm as well as good. Education seems like it might be an example. Let's suppose that in fact Gates is a total saint, motivated by nothing but pure benevolence. Does that make someone whose education was worsened by the foundation's activities any better educated?
I find I don't really care very much whether Gates is a good person, for any particular definition of "good". I care about the effects of what he does. Maybe he's giving his money away to make himself look good, or for a bet, or because he hopes it will placate an angry Microsoft-hating god, or something. Who cares? What matters is what actually happens as a result of his giving that money away.
