Boys, boys, boys. Men want sons, and Michael was no exception. Let's face it, this was a dangerous business. Vito probably felt reassured when he had THREE, but look what happened - Sonny's dead, Fredo's, well Fredo, and Michael has to take over. Tattaglia lost a son, I'm sure many families did. Although Michael adored his children, on some level, he may simply have been stocking the shelves by wanting more sons.