I think those are two separate questions.Why is courage a virtue? Why isn't cowardice a virtue as well?Why is courage a virtue? I think because society/culture most likely made it that way.I'd also bet that it was a Darwinian process, and lager groups of people, under a homogenous culture, were more likely to stick around by promoting individuals who practice courage (selfless behavior/thoughts) with positive reinforcement, while those who practice selfish behavior are discouraged with negative reinforcement.To use the grenade analogy:There are 10 soldiers in a small empty concrete room, with a live grenade. If 1 guy jumps ontop of the grenade, he ensures the safety of 9 others. Assuming you're in a position where selfless cooperation is a benefit (ie, 1 guy enveloping a grenade with his body), that self-sacrafice could actually benefit his genes and the group's genes. So in a Darwinian sense, it's probably an advantage being able to convince people to do things like march into machine gun fire, where self-destruction is more or less assured, so long as you judge the "economics" of the risks/payoff correctly (eg, never gambling the whole-groups existence unless forced to do so).