I've long been amused at people who tell you what you "should" do or "shouldn't" do. Occasionally I've been annoyed. Always I have challenged them back on these declarations, asking them
"Who decided that people should do this?"
"How did you come by this information?"
"How do you know with certainty that this is right, and others who believe the opposite are wrong?"
This tends to aggravate the individuals prone to moralizing and polarizing to no end. They become flustered and upset. Sometimes they will respond to you and tell you that you are being morally relativistic, and that moral relativism is wrong, because clearly there is a clear black and white, right and wrong, good and bad in the world.
When asked to explain why heroes to some are villains to others, and villains to some are heroes to others, they simply stutter, stretch, and eventually use blanket statements to cast entire civilizations of people as "wrong," never understanding that the members of the very civilization they call "wrong" would call them "wrong," too.
Rather than engage in lengthy, unending debates with these people these days, however, and spend precious time trying to convince those who are so certain their views are right that they are viewing things too closed-minded and too far to the extremes, I prefer now to just tell them one simple thing that cuts to the heart of the matter as best I know how:
Your mental model is flawed.