I could bet money that, even if you work for free for this corporations, and prove to be a good asset, when you will ask them to be hired, because you need to pay rent/internet/electricity/etc..., they'll answer you
"We're sorry, Joe, but unfortunately your resume and skills don't match what we are looking for, bla bla bla...", well, actually, my resume will never match your target, because you spend, what, 10 seconds reading the first few lines of it?
or even worse they answer
"Unfortunately we can't afford right now to hire you, bla bla bla..."
I really hate the approach of many corporations, that think they are doing you a favour when they hire you.
Volunteering for non-profit projects, like Wikipedia, is great, but doing it for evil corporations is the worst thing you can do to make the world a better place...