Yes, Vito's attitude was not to interfere. But, if Carlo had complained to him about Sonny, he probably would have said, "What goes on between you and your wife is none of my business. Now you've made it my business by complaining to me." He would have lectured him about being a real man, along the lines he lectured Johnny Fontaine, except more forcefully. I think he would have been much harsher with Sonny--not only for interfering between a man and his wife, but also by exposing his temper--his main weakness--in public, which Vito would have known would lead to a bad end.
You're probably right TB. However, Vito's indifference to Connie's suffering is one of the most disturbing parts of the novel. Equally disturbing was Vito's apparent admission that he would have beaten his wife if she had given him reason to.
In a way, it's not surprising. Afterall, he was willing to drag his sons into his murderous way of life.
