Hasn't this been discussed before? The Person of the Year award is supposed to be given to the most influential person of the year, not the nicest or the most ethical one. Zuckerberg did become a widely recognizable person and you can't say he has not become influential too. Joseph Stalin got the award twice, 'nuff said.
Disclaimer: I'm not comparing, just pointing out that the FSF's reaction is kind of attacking the straw man here.