serial killers

All humans are accidental serial killers.

We step on ants with zero regard, we smack a fly and enjoy it, we squash a spider and feel accomplished. Yet we jail people who kill rhinos or elephants and we think people who kill cats are psychopaths; yet we all kill insects all the time (whether intentionally or unintentionally).

So why is this the case? What defines when a murder is ok or not ok?

Is it the size of the animal?

Is it the way they look?

Is it their character when they interact with us?

Is it their intelligence?

Is it how much we can relate to them?

Is it the amount of danger or nuisance they impose on us?