In Nagel's paper "War and Massacre", Nagel attempts to limit utilitarianism. Utilitarianism is the view that as long as the greatest number of people are benefited by an action, this outweighs the negative consequences for a few people. The question is whether there is a limit to the extent of the negative consequences that a few can suffer in order for an action to be morally good. Nagel argues that there are some negative consequences that are always wrong, no matter how many people are benefited by an action.
Utilitarianism & Absolutism. Utilitarianism is the view that an action is good or bad based on the consequences. Absolutism is the view that an action itself is good or bad. Absolutists do not think that the consequences alone can justify an action that is bad in itself. Absolutism does not ignore consequences of an action. Absolutism is a limit of utilitarianism, not a substitute. Absolutism is the view that while consequences are relevant to the morality of an action but that some actions are always bad, regardless of consequences. For example, innocent murder of civilians is always bad, even if it brings about good consequences.
Two Restrictions. Nagel argues that whether war is moral depends on how the war is fought. Some things should never be done in war, such as murder of innocent civilians and killing medical personnel. There are two kinds of restrictions of behavior. First, only certain kinds of people should be attacked. For example, only soldiers or paramilitary armed fighters can be attacked. Children and other innocent civilians cannot be attacked. Second, only certain kinds of attack are acceptable. For example, it may be OK to shoot someone, but it is not OK to torture someone or poisoning a water supply. The first is a restriction is on the class (or kind) of people to be attacked and the second is a restriction on the type of hostility that can be used.
Nagel's point is that we cannot only consider consequences when deciding if an action is moral or immoral. Some actions, Nagel says, are bad even if they provide good consequences.