I'm kind of "on the fence" about this topic.

I will say this - When were Kay and the children in danger ?

Since when are the innocent wives and children of gangsters in the American Mafia put into the line of fire ?
I'm sure there are instances, but they are few and far between.

Michael said this to himself so often, that he eventually believed it. He had to blame someone, but he could never actually blame homself.

I do believe that Michael believed he had no choice. However, I agree with Turnbull, in that he had a window, albeit a short one, to escape the life while Vito was still alive.