If George Clooney denounced DRM/a patent troll/baby killing, would the denouncement be any less valid? Celebrities may not be experts, many of them may even be idiots, but if they use their celebrity to promote a worthy cause rather than themselves, that's a good thing. When they lead action for that cause, that's even better.
He's a computer freedom activist. Worked for the EFF, anti-DRM campaigner, etc. Not that anyone should need special qualifications before they stand up for their rights.