I believe that Amsterdam did have the intention of killing Cutting from the beginning for the reason of avenging his father's honour. However, it does appear that Amsterdam was conflicted in whacking The Butcher (at least until the end) because of how close they got. The Donnie Brasco parallel is an interesting way of looking at it but I think in D.B. it was taken even further as Donnie was so wrapped up in Lefty's world that the emotional attachment was very strong. On a completely unrelated note, director Martin Scorcese makes a cameo in G.O.N.Y. In the scene where Jenny Everdean (Cameron Diaz) dresses up as a maid to rob a house the father of the family eating at the table is Scorcese.