I don't think that it was Puzo's point of view, only his writing which reflected the general opinion of the time I guess.
1) Puzo's parents came from Naples, not Sicily
2) In Sicily too a ladies'man is a real man, and he takes care of his family too. And of his mistresses as well.

I think that Puzo's writing just aimed at showing how weak and "mentally retarded" Fredo was (due to an illness he caught when he was a baby). It was Puzo's way to translate Fredo's dependence on women : he never grew up into a man, he remained "always at its mother's nipple".

"Come heavy or not at all." Uncle Junior to Tony S.
"Nenti dire ca nenti si capi" come disse quello. (Say nthg when U know nthg.)
"Chi non ci vuole stare, se ne vada." (If U don't like it here, go somewhere else.)