Two things stuck out to me today.
First, some gun violence. One is a report of a veteran known to suffer from PTSD who snapped and shot at someone at a mall. Police (armed) stopped him. The second is a shooter in a high school with metal detectors - just today. An armed guard stopped him - not the metal detector.
Shootings aren't prevented in gun-free zones. The good guys with guns stopped the shooters in both (and most) cases.
Second, mental illness continues to be in the forefront of violence. A psychiatrist who has worked for the prison system in various places estimates that a full 2/3 of inmates have mental health issues. A good chunk of that 2/3 incarcerated with mental illnesses are pyschopaths: unable to feel remorse, compassion, or empathy. Those with violent thoughts and intents should be locked up even before they commit crimes for the good of society, but sadly that is not the state of our mental health system or judicial system.
If we in the United States are serious about preventing casualties, we had better think of reforming the mental health care system rather than gun control. Laws do not prevent people from getting guns if they really want them. The ones we want to prevent the most are the ones most likely to find them and use them illegally! I've talked about these things extensively before.
Preventing good guys from getting and using guns in self defense and the defense of others will not solve this problem. Talking about mental health, erasing the stigma against it, and reforming the system to make it easier to get care to the people who need it will go a long way.