He didn't want to be a 35 y/o WR looking for a new contract who hadn't played in a year. If the Pats weren't going to give him a contract, he wanted to play for someone who would. I'm not going to begrudge him that: he wouldn't have foreseen the lockout when he signed his extension with the Pats, and that changed things. If the Pats had given him a better alternative, we can only guess that he probably would have been fine.
It's a business when the Pats cut a player who's under contract, and I don't hold that against the team. Likewise, I don't hold it against Moss that he has a family and a post-football career to look out for. He gave us one historic year and 2 other great ones, so I'd much rather thank him for the 50 TDs and hope the team can pull together and do fine without him.