Just to add a nuance to your post, Don T:
One of the durable myths of the Mafia is that they "only kill each other." Yeah, sure! We see that in the Trilogy:
Early in GF, when Michael plans to go to NYC to visit Kay, Sonny wants to send bodyguards with him. But Clemenza says, confidently, that they're unnecessary because "Sollozzo knows Mike's a civilian." He's ready to entrust Michael's life to what he assumes is Sollozzo's sense of "honor," even though Sollozzo's just attempted to murder Vito. But by the end of the film, Michael's gunmen not only murder Tattaglia and Barzini, but (as you note) the other two Dons. And while they were at it, they whacked a hooker with Tattaglia, a bodyguard and a chauffer (who may have been a civilian) with Barzini, and probably the elevator operator and another guy in the elevator car with Stracci (I doubt anyone could have survived two shotgun blasts in a small space like an elevator car). In GFII, Roth's gunmen spray Michael's bedroom with machinegun bullets, obviously not caring that Kay was there, and possibly Michael's kids as well.
In the most egregious example: In GFIII, told that Sicily's top assassin--"a man who never fails"--has targeted him, Michael goes to the opera and sits in a box surrounded by his family, making them sitting ducks along with himself. The miracle is that only Mary was killed.