A people about to cross into hostile territory cannot afford a fractured chain of command. The severity here reflects the deadly stakes of a body of men who must move as one or die scattered. Rebellion in that moment is not brave dissent but a threat to everyone's survival. Break ranks and the whole company bleeds.
Courage gets the last word for a reason. Strength is demanded of the leader and obedience of the followers, and both are forms of the same thing, which is the willingness to act under threat. Order held together by shared resolve is what carries a frightened people across a river they would otherwise never dare to cross.