What is it they said, "keep your friends close, but keep your enemies closer"...
Bottomline: Fanucci was killed otherwise you don't have The Godfather, or The Godfather Part II.
Remember young Vito (DeNiro) lost his job, to who? Fanucci's nephew.
Here is the death scene, no dialogue just music:
I know for a fact during The Godfather, that Irish American Marlon Brando, personally got so drunk at the wedding reception of "Carlo and Connie", and he insulted many of the Italian American extras "attending" the wedding, a fight broke out. He made fun of the way Italians talked and gestured. A mobster threatened Brando and vowed to put a contract on his head. Francis Coppola had to "negotiate" with the soldiers of the Genovese family in attendance there. After that, all scenes had no hard alcohol, just beer, tea, and water.