If you NEED a manual safety in place of the one between your ears, YOU are the idiot and should not own guns.
Ever walk into a room and forget what you were looking for? Even misplace your car keys or wallet? Ever trip and fall on something you didn't see or bump into something by mistake? All humans make mistakes. Especially when tired, sick, feeling down, stressed, excited, in a rush, etc. Unfortunately training can only decrease your chances of an AD, it can never make them 0%. On a long enough time line every single person with a gun would have one. A manual safety decreases your chances even further. The human brain is NEVER going to be enough to decrease your chances to 0%. Now if you can show me some research showing me that humans never make mistakes, that our mind never wanders, etc I will believe that snake oil you are selling but come on that statement is some real bro science.