Of Mice and Men may be about men full of masculine bravado, and there may be some pretty shocking violence, but these guys also inflict psychological and emotional violence as though they're auditioning for Mean Girls: The Musical. Violence in the novel is physical, psychological, and emotional. Characters are so accustomed to suspicion and failure that they treat each other cruelly, more ready to destroy each other's dreams (and bodies) than to build them up. Violence may be a natural outlet for all of the ranch's despair and limited possibilities, but it sure does make the world an ugly place.
In Of Mice and Men, physical violence is more severe than psychological violence. The men simply don't spend much time worrying about their psyches.
Steinbeck suggests that violence is a necessary part of justice.