Plato was impressed with the idea that he who can best heal is he who can best kill. I doubt it. The big brawny person with the nail-studded club can kill as well as a physician. But a weaker claim seems plausible: those who are competent to make one well are competent to make one unwell. The reverse is false. Competence with clubs and poisons does not imply competence in surgery and healing drugs. Similarly, it is easy to completely destroy a car and hard to be a mechanic. The asymmetry is interesting. It suggests an important asymmetry between good and evil.