They lend their face and their bullshit smile to the government towards which many people have a much more healthy distrust. I agree that this doesn't make them the main culprit, but they don't get to completely wash their hands of it either. Big (monstrously huge, actually) corporations make the job of tyrannical governments much easier; how about we chop them into more manageable bits without having personally hard feeling towards them, and deal with the government(s) at the same time?
No, it's absolutely productive and helpful. We the people have no voice. Companies like Google who makes billions are the ones with a voice. If a million people left Google in protest you could expect action. If a million people signed some bullshit online petition nothing at all would happen.