Seems like it's just fanboyism and they can't stand that a band they care about (or at least enjoy) has sold out to the absolute worst degree. People are right in that all bands sell out to a certain point ("All you know about me is what I've sold ya, dumb fuck/I sold out long before you'd ever even heard my name/I sold my soul to make a record, dipshit/And then you bought one" -- Hooker with a Penis, Tool), but when you specifically accept a gig that is just some elitist executive party for a company that treats its employees like shit, you've gone too far.
Fuck the Foos. And stop making it political ("lol, liberals") -- bullshit, this is just rampant band fanboyism.