Our moral sense licenses aggression against others as a way to prevent or punish immoral acts. That is fine when the act deemed immoral truly is immoral by any standard, such as rape and murder, and when the aggression is meted out fairly and serves as a deterrent. The point of this chapter is that the human moral sense is not guaranteed to pick out those acts as the targets of its righteous indignation. The moral sense is a gadget, like stereo vision or intuitions about number. It is an assembly of neural circuits cobbled together from older parts of the primate brain and shaped by natural selection to do a job.
Pinker, Steven. The Blank Slate: The Modern Denial of Human Nature (p. 270). Penguin Publishing Group. Kindle Edition.
And so that moral sense is a sword with a double edge. On the one hand, it helps maintain a society. On the other, it also licenses the suicide bomber and the assassin of politician you disagree with.