TB, I think the fact that many do argue that it was just "poor Fredo" and that he didn't deserve to be killed, is a credit to Cazale's excellent acting. It was not an easy role to play, and he did it superbly.
Exactly. Remember "U'm gonna learn [shrug] the casino bizness." That shrug was so cool and fit him so well. And I bet that he thought finally I'm gonna do something really important for the family.