Difference in attitude about personal defense
Dwight55 covered it well in post #3.
I've lived in large urban environments and isolated rural areas. My attitude towards self defense hasn't been influenced by my address.
The general rule is "stay out of third party situations."
There are far too many variables that I (or any other CHL holder) do not understand in the vast majority of these cases to justify our application of deadly force. That's not to say that if I were on location during a mass shooting that I wouldn't take action. But it would have to a very obvious case before I'd make the decision to intervene.