A massacre is an indiscriminate killing and is of little spiritual value except to alert us to the violence of others’belief.
Psychological / Emotional Perspective:
Indiscriminate killing in dreams suggests that emotions have been allowed to get out of control and taken over from reasonable behaviour.
Everyday Material Aspects:
In mundane terms, when business methods become both heartless and ruthless this can be translated into dreams as a massacre. This may also suggest that there is little we can do personally to prevent this.
You might like to consult the entries for Death and Kill.