I had this very interesting discussion on the article Malum Prohibitum. My opponent was stressing that I had no right to declare any crime as malum in se (wrong or evil in itself) because I could not present an objective point of reference as to what constitutes right and wrong.
In law, a crime can be categorized as either malum prohibitum (“wrong because prohibited”) or malum in se (“wrong or evil in itself”). In a civilized community, murder, rape, theft, robbery, and kidnapping are generally perceived as mala in se regardless of where they were committed or even if there were no written laws punishing them. On the other hand, illegal possession of drugs or firearms and traffic and tax violations are mala prohibita – crimes in certain societies because their statutes made them crimes.