You can believe anything, just accept it's true and build a set of explanations around it.

One interesting ability of an animal brain, is to believe contradictory things by compartmentalizing away different beliefs into separate contexts. Cats for example can believe that "human legs on a checkered floor = danger" while "human legs on wooden floor = friendly food source", and act accordingly.

Humans, like to believe their own mental processes are perfectly integrated and coherent... but they're not; they're more abstract, but equally context related. It takes a conscious effort to break those contextual barriers and come up with generalized "moral rules", which most people simply don't do.