In fairness to Vito and perhaps even Tom? they may not have known? about Sonny's public beating of Carlo However

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Originally Posted by Lana
Vito had such contempt for Carlo yet he allowed Carlo and Connie's marriage to go ahead
Vito giving Carlo just a living “Never [give Carlo something important] Give him a living but never discuss the Family business with him”

This failure of Vito, made the low life parasite, wife beater, resent so much so that Carlo was beating Connie even when she was pregnant and setting Santino up to be murdered albeit revenge for Santino's public beating and humiliation of Carlo which may not have happened if Carlo had been given something important

If anybody is to be blamed for Sonny's death it is Mama! for passing Connie's phone call onto Sonny