When I was a cop in Oakland, CA in the 70's, then as now crime was rampant. There was one liquor store in N. Oakland that almost never got hit, at least it didn't during the 10 years I was there. Word was out, in the department and on the street, the employees there were armed and a couple of would be robbers had died there. Arguably, and by case law in most states I'm aware of, when a robbery suspect has a deadly weapon there is a presumption he may use deadly force during the commission of the crime. Using deadly force to defend oneself is thus justified. Most states do not extend the justification for use of deadly force only to protect property.
Still, how much looting and rioting do you suppose there would be if the first one or two torching a building or carrying out loot took a round?