Yes, Fredo did show genuine remorse in the boathouse scene. And even more so at mama's wake. However, that would not have prevented him from committing another betrayal against his brother...even if many years later.

You mean an 'inadvertant betrayal' like the one that nearly had him and his wife killed and the Corleone Family brought to its knees to be overrun by Hyman Roth? A betrayal like that which Fredo might not have realized was a planned hit?

Michael was definitely justified in having Fredo killed...and I don't believe it was for revenge. It was to have him punished for what he did, and mainly to prevent it from happening again. As I've said here before (and will say again whenever the need arises)...had they not been brothers and shared the same mother, Fredo the traitor would not have been allowed to live even as long as he was. And I doubt a soul on this BB would have a problem with Fredo's fate.

After all, their blood relation sure didn't prevent Fredo from conspiring behind Michael's back. So why should it prevent Michael from bestowing on Fredo the usual fate of a traitor?

Which of course, he didn't know was coming... !!

Apple