In what episode of TNG was an ancient Vulcan psionic weapon discovered? If I recall correctly, the device had 3 parts: life, death and balance in between. It worked only against aggression (to the best of my recollection).
The episode that featured the device was called Gambit:
The artifacts are part of an ancient Vulcan telepathic weapon, the Stone of Gol. Picard realizes the true nature of it, once a powerful weapon but utterly useless against people who don't bear aggressive thoughts.