But we're not talking about the crusades we're talking about something that you suggested could be "understandable".
We need to use our sociological imagination to see why people behave or behaved the way they do. For example, when we consider the persecution that the utah saints previously experienced and the threats that the utah saints were still experiencing, we may understand that a small group of Mormons felt threatened by the fancher party. Of course there was no threat. But...psychologically, there can be an explanation of mistrust, fear, anguish etc.
After so much suffering in the past, and the suffering that the saints experienced on their journey westward, well, some may not have been the most psychologically fit.