This whole defense argument is seriously flawed. People seem to have the odd notion that if they are attacked they will prevail. But how can anyone think that when the armed security guard who tried to shoot the Buffalo shooter died in the process. And security was not only his job, but he was retired police and therefore had much more training than the average gun toter.
I read today of an armed bystander who heard shots in a mall and positioned himself to shoot the shooter, but was seen and killed by police.
The fact is that people out to kill have the advantage of surprise, and a lot of them seem to be using body armor. In order to protect yourself from such rare occurrences, you would have to ensure your gun is with you, loaded and ready to use at all times. A level of paranoia that is hard to even imagine. And hope the police or other bystanders don't mistake you for the aggressor.