Fair enough for an opinion.
However, I can assure you that many violent criminals don't give hoot if someone is carrying a gun. Most of them have them too and as a violent criminal, they are more likely to use it.
The key thing works if you already know how to defend yourself. If you think the flailing wildly with your keys will help you are wrong.
The inner city thing is a bit harder. I used to be part of a gang so I understand the mentality. There is a distinct lack of fear of anyone else having a gun. They understand the repercussions of shooting someone in a way vastly different than anything most people can understand. They don't fear jail. They don't fear the police. They don't fear another person with a gun. Shooting someone and being shot is a way of life.
In that situation the more guns out there the worse the violence will become. I've seen it happen.