Eh fanboys... give'em blogs & forums and they'll sure make some noise. Besides, the "anti-capitalist" part sounds more like a political/ecnomical opinion rather than something related to Mono or Microsoft.
BTW, I wrote an importer for a game and thanks to Mono it runs on OSX. Neat.
I would think MS fanboys would cheer Mono, because its a way to prove Microsoft isn't trying to control development or limit cross-platform code.