Obviously there are multiple effects of having more guns around. A lot of people have opinions on how big these different effects might be, but the research into the consequences of gun ownership has been starved of funding for a long time, so as far as I can tell no one really has a good handle on it. It may well be that it makes more sense to arm everyone in Detroit than most other places, but personally I don't have a lot of confidence in people's decision making under stress.