Clearly you did not read what I said.
Cops may not exist in the novel, but there are groups similar to cops.
Murder may be condoned in the novel, but there are spiritual forces that enforce punishment on murderers.
If you're the MC, hope you're an OP MC, because if not, then just killing pests left and right anytime in anyplace will just invite more bigger pests.
In short, kill if you're willing to accept the consequences of your action. Some MC do that, others don't. It's that simple, but of course, sometimes the author forgets to add the consequences of murder in their novels.