“The Godfather Effect” is a study of the trilogy by Tom Santopietro which shows that the Italian characters in the films were portrayed as real human beings instead of stereotypical caricatures who spoke with heavy accents. This had a positive effect on the American culture which had considered the Italian immigrant as "the other".
The film and its sequels are most famously remembered for romanticizing a mafia family and their crimes to stay in power. Even though the characters are realistic, the trilogy still reinforced the stereotype about Italians being likely involved in mafia affairs.
[P1] Italian-Americans saw themselves represented as real human beings instead of caricatures to be mocked. [P2] Americans' acceptance of Italians immigrants and Italians-Americans was increased. [P3] Movies can have an impact on the real life perception of individuals and groups.
Rejecting the premises
[Rejecting P1] The trilogy reinforced the stereotype about Italians being often involved in mafia affairs. The first film was boycotted by the mafia in NYC until the producer made an economic agreement.
John Patterson explains how the mafia tried to shut down the filming of The Godfather  'The Godfather Effect' by Tom Santopietro By Daniel Bubbeo  The Godfather Effect: Changing Hollywood, America, and Me