The fans and team have every right to be mad at him. He waited until the team has no opportunity to get another starting QB to retire. He screwed the team first the season. Not intentionally, but he did.
Now that being said, if he is just tired of the pain and hurting, he has every right to hang it up. No one should question his right to do it, he just couldn't pick a worse time. It will just look worse in the media because he doesnt have a "career threatening" injury.