OK, I think I see what you mean. When Michael says he wants to be redeemed and sin no more, it's a given that he wouldn't want to do anything evil enough to sentence himself to hell -- not even if that something evil will protect Mary or Anthony. But I certainly don't think that means "the heck with protecting Mary." It simply means he won't use evil means to protect her, or anyone.

All in all, those are just words, and Michael's words don't kill Mary. It's his actions that cause her death. And note that Michael's actions are the opposite of his words. "By asking for a chance to redeem himself, he is no longer going all out to protect his daughter." On the contrary: He breaks his vow to redeem himself so he CAN (in his mind, anyway) protect his family (among other interests).

He sanctions murder through Vincent, giving him the order to kill his enemies so his family will be safe. The irony is that Michael has rationalized murder before by claiming it was to protect his family and it has NEVER protected them. It has only led to more endangerment and more murder. Michael fails to see that the true danger is his consorting with dangerous criminals. If Michael had gotten out of the mafia business in the first place, Mary would never have been accidentally killed.