Carrying a gun is a good thing, provided one is well-trained as to not only how but when to use it. Cops can get away with shooting someone defensively (or allegedly so) mainly because cops are required to take a defensive stand in combative situations. Civilians are not.
In most states, a civilian is permitted to use lethal force only if there is no opportunity to "retreat" to avoid violent confrontation. The only exception to this rule I am aware of is Florida because of its ground-breaking Stand Your Ground law.
So with that singular exception, a civilian who carries and uses a gun had better be ready to explain why he/she had absolutely no means of retreating from the threatening situation and there was no alternative but to use lethal force against a menacing aggressor.
I hate to break this to you, Mike but Stand Your Ground statutes exist in many more States than just Florida...
- See more at: States That Have Stand Your Ground Laws - FindLaw