that he chose not to avenge his son, and you may praise his dedication to peace all you want, but at the end of the day what the other dons saw was a weaker don, like Michael told him "a sign of weakness".
Well this one of those things that you definitely have to read into....
"a sign of weakness" by Vito was more a part of the big picture, the master plan. When Michael says(in deleted scene) "Isnt promising not to break the peace a sign of weakness" Vito says "Yeah".
BUT.... you could easier insert the following lines.... "Yeah... but I had to get you back here safely and buy us some time to get all of our ducks lines up" You are our last hope... after all "Fredo...well... Fredo is... Well Fredo" LOL
Vito didnt want it for Michael... but Michael lets him now "I'll handle it" very adamately I might add.
