How is he being "anonymous" when he uses his real name? Also, none of you have ever been critical of any athlete? You've never "booed" at a game when your team isn't playing up to par? You've never said a player isn't good, or one is better than the other, or why can't Player X stop doing (fill in the blank)?
Of course all of us have, but would you say those exact things to that athlete's face? Probably not. So then how is doing that ok, but you can't tweet something or post it online? Is it because that makes it more public and you are only allowed to criticize privately? I really don't see the difference.