Even if they can be trusted with a gun, even if they pull it out to save the day in a crisis…
There’s still projectiles flying that could hit people and things other than the intended target. That’s the part that it always comes back to for me. Bullets aren’t target-seeking. Even the best and most well-meaning shooter can miss in a stressful situation (especially with a handgun), it doesn’t mean they’re a bad person. It just means adding a gun to any situation complicates the situation violently. Adding multiple guns multiplies the violence.