Earlier quoted context omitted.
How we should treat the "animal" that kill people then?
All humans are capable of horrific acts. It is a part of our humanity, we are apex predators who organize socially. The evolved algorithm in our brain that manages that dissonance is extremely complex and will necessarily fail at times. We can't tolerate or condone antisocial behavior, but it is a mistake to feel safe in the thought "we" are better than "them." We are they, they are we.
This, so much this.
It's so easy to turn it into 'us' and 'them'
So many stereotypes, so much historical(and, of course, current) violence and bloodshed because someone convinces a population how 'they' are different than 'us', 'we' are better, therefore 'they' must surrender(and become like 'us') or 'we' will force 'them' to.
My favorite example? Extrajudicial killings of non-us citizens unilaterally declared to be terrorists. And since it's 'them', somehow it's moral. Terrorism is bad, but doesn't give us the right not to afford another human the protections of things we have declared to be owed to all men.
If 'We hold these truths to be self evident..." then why do we only apply them to US Citizens? (And then, take them away from some US Citizens, the ones that have been declared to be 'them' no longer 'us')