A View from the Bridge sets up a very basic conflict: "civilized" American law vs. "uncivilized" Italian tradition. When the American justice system is incapable of bringing the characters the kind of justice they think they deserve, everything goes haywire. They resort to their unspoken codes of their Italian roots. This results in stuff like bloody revenge and duels in the streets.
Marco is right to kill Eddie in the end, whether it's against the law or not. Eddie gets what he deserves.
Alfieri is a first generation Italian American lawyer. This makes him the perfect embodiment of the play's clash of cultures and their differing ideas of justice.