but it's not a law of physics that the feudal lord kills a peasant - they did it by choice. This is what absolves the rebels from any guilt of the deaths. The rebels, a priori, believes that their rebellion is just, and therefore, by definition it cannot be morally wrong. It's not their fault if the feudal lord decides to do something morally wrong, based on any reason (including to extort the rebels).

This is different from a case where actions of the rebel directly lead to deaths of peasants - for example, bombing the residence of the feudal lord which causes collateral damage. In this case, the action must be judged individually.