They could have acted differently. What they did was wrong; I wouldn't have done that; they could have done something else.
I would posit that the chance for something to have happened differently than it did is 0% - since something would have to change about the situation in order for it to happen differently. It’s legitimate to try to learn from history in order to act differently now or in the future, but saying that someone should or could have acted differently than they actually did is imposing unrealistic expectations on them. They acted how they thought they needed to act; they would have to have been different to act differently - and they were who they were, doing the best they could, while dealing with what was in front of them at the time as they, like us, saw through their own glasses, darkly.
I am positive my own descendants will look at much of what I have written and said and wonder how I could have believed such silliness. I only hope they realize that I "shouldn't" have acted or believed any differently than I did, since I did the best I knew how.