I wonder if the brother’s last words were “oh, wait...”
One argument I've heard for total confiscation of firearms is to save lives. Unlike other means of suicide (overdosing, head in oven, etc.) one can't change their mind after they pull the trigger. Supposedly, many suicidal people do have second thoughts. Plus, maybe mental health treatment is a better way to prevent suicide...
I am not an advocate of gun control based on that or any other logic, by the way.