And even if Vito had caused the resentment that Michael did or Sonny caused the resentment that Michael did and their brother did something dangerous because of the resentment that they may have caused, stupid, but dangerous, I still do not believe that either of them would have ordered the death of their own brother.

And truth be told, it actually was Vito, more than Michael, who caused a resentment to build up in Fredo. He chose Michael to be his successor. It's the way POP wanted it. In fact Michael probably gave more freedom and responsibility to Fredo thatn both Sonny and Vito combined ever did!

Of course Fredo was envious of the power that Michael was given over the family. But Michael should have shown a bit more compassion and understanding. This was his blood brother, his mother and father's son. Not some enemy from another family.

It was Michael's paranoia, his having to show the others around him that he was the all powerful DON who would tolerate nothing, that played an integral part in his making the decision to do away with his brother.

It was a horrible decision. And that decision played a huge part in Michael's inner decline.