The Economics of the 2nd Amendment
I don’t think I could say it better, so I’ll just let David’s words stand on their own.
“Suppose one little old lady in ten carries a gun. Suppose that one in ten of those, if attacked by a mugger, succeeds in killing the mugger instead of being killed by him — or shooting herself in the foot. On average, the mugger is much more likely to win the encounter than the little old lady. But — also on average — every hundred muggings produces one dead mugger. At those odds, mugging is an unprofitable business — not many little old ladies carry enough money to justify one chance in a hundred of being killed getting it. The number of muggers declines drastically, not because they have all been killed but because they have, rationally, sought safer professions.”
— David Friedman
Source: Hidden Order: The Economics of Everyday Life (New York: Harper, 1996), p. 299