When you badmouth someone or talk scornfully about them (especially when they don't deserve it), that's denigration. If you practice denigration, shame on you!
It's one thing to criticize people fairly, but when it's done in an unfair or unnecessarily hateful way, it's not criticism — it's denigration. The denigration of a public political figure is bad enough, but the denigration of ordinary people because of their religious beliefs, sexual orientation, or body size, for example, can even be illegal. Denigration is rooted in the Latin denigrare, meaning "to blacken."