Unlike a pitcher purposely throwing at a hitter, I don't think Utley's intent was to injure anyone. His intent was to break up a double play and do what is necessary to win a game the Dodgers desperately needed.
As mentioned before, I thought it wasn't a great decision on his part the way he did it and it wasn't necessary, but as sometimes happens, even the wrong play can turn into a winning play.
Bottom line, in my opinion, it was unnecessary. If that is called legal, the rule needs to change.
I don't think there will be any retaliation by the Mets, unless it would be something they think will help them win a game. Then again, it might be interesting if Utley had to turn a double play.