There's no way I would have let Carlo live. In a hypothetical setting if I had Michael Corleone's power, it would simply be an impossibility to let the man responsible for my brother's death escape swift and brutal retribution, regardless of him being my sister's husband. In addition to this, letting Carlo live would pose a direct threat to the family based on his treachery and his disrespect for the Corleones.
Just thought it bears mentioning again.
And for the record, 'if' I were "Michael"...I would not have let Fredo live, either.
Apple
I understand that Michael is a mob boss and that his brother, a person who is someone he should be able to trust with his life, betrayed him. In a situation where Michael felt that Fredo was a direct threat to him and a direct threat to the Corleones, killing him need not be the only solution. A permanant exile, or even forgiveness could have been other options. Although this would run contrary to the utterly ruthless nature of Michael and in order for the viewer to feel this intense ruthlessness Fredo had to be killed. I believe that
Mario Puzo and F.F. Coppola were divided on this issue and Coppola won out.
On a personal level I couldn't fathom any circumstance of killing my own brother, ever.
