Why are Italian Americans so proud of their Italian heritage when Italy rejected them?

The overwhelming majority of so called Italian Americans are actually from Sicilian or southern Italian decent, the reason they came to America was partially due to the rampart racism, most Italians considered Southerners and Sicilians to be dirty because of their middle eastern and black blood, so why do I see so many Italian Americans waving Italian flags(in America for cryin' out loud)and boasting about their Italian heritage?