He chose to go to Arsenal so he is our rival now. Doesn't matter, if he was part of our academy, he is playing for our rivals which means he is directly competing against us. I wish him to fail quite hardly actually because that will be good for United, the club I support.
I never get you people that wish Welbeck to do well at Arsenal... Seriously? Are you supporting Danny Welbeck or Manchester United?
EDIT: Welbeck doing well is detrimental to us as proven in Arsenal last match where he gave them the 3 points. If it wasn't for him, we could have been 4 points up now. He gave them many points now which is hurting us.
Also, I don't hate Welbeck for choosing Arsenal, it was his decision and I think every player would have chosen Arsenal over Tottenham, but there is no way I''m supporting him either way.