In your paper, touch on the basic points. Vito exists within his own world, the criminal world. He does not believe in society's laws nor in its justice. Vito believes that no good deed should go unrewarded, while no evil deed unpunished. I think that due to the fact that he operated a criminal empire is what makes him an anti-hero. On these boards, many (myself included) tend to glorify Vito Corleone and we sometimes overlook that his brand of "justice" involves murder, bribery/corruption, illegal gambling, and using the threat of, or actual use of, violence to intimidate others.

I think if you read the novel you can get some more background into Vito's psyche and how he became to be the character we know.