There's certainly no shortage of wannabee cowboys posting here. It's a sure bet that not a single one of you has actually had to confront an active shooter with scores of innocent bystanders nearby. When the police, who are supposedly trained for these scenarios, encounter them, their intended-target hit rate is typically 25% or less, and they tend to hit innocent bystanders on a regular basis. They also have a habit of misidentifying the "good guy with a gun" and shooting him instead, especially when said good guy isn't white. See Hoover, Alabama for a recent example. Ask yourself if you really want to have a gun out in a situation like this when the popo show up. They're at least as likely to take you out as they are to get the "bad guy with a gun."
As for the "lone nutter" fantasy, that's blown entirely out of the water by the gun-totin' nutters who post here. I wouldn't trust a single one of you any further than I can throw you. You provide compelling evidence in favor of universal background checks....