Criminals are the human version of the Predator in nature. Being a predator is hard work, that is why they work hard to single out the weak and old, since they represent the most gain for the least energy expended. They will instinctively avoid creatures which represent (a) too much work, (b) too great a threat.
An armed Citizen fits into both groups. That's why crime is high in areas of high gun restriction; the government of those areas makes it easy for predators to operate. Areas where gun restrictions are low also have low crime rates; the people there are too great a threat to the predators in human society.