How does collective violence become moral?

By virtue of the fact that people attach to a SACRED OBJECT, which converts killing and dying into righteousness.

Sacred objects are imaginary entities that “transcend” ordinary life.

In ordinary life, people make a BIG DEAL when even a single person or a few people are murdered.

Yet in war, massive killing is commonplace and taken for granted as an ordinary part of “reality.”

Why is this the case?

Because this collective killing is done in the name of a sacred object (the nation, god, Allah) that converts killing, dying and atrocities into moral acts.