No, there is never a valid, meaning socially acceptable, reason to become a serial killer. Though, the theories build why some do are quite interesting. One reason this modern lasseis-faire (forgive me, I can’t remember how it’s spelt) attitude toward cops killing serial killers and mass murderers is that they are of no scientific use when they’re dead. Once they’re dead, we can no longer study them and determine the why behind it all, and that reduces our chances of finding a way to prevent these atrocities from happening.