I've been training in a grappling sport (BJJ) for over 9 years. The advantage a trained person has over an untrained one is massive. Even someone who has been training a few months could easily handle an untrained person without anyone getting hurt.

You can see hundreds of videos out there of police shooting people without apparent just cause - just because they "felt threatened". If they had the confidence they could deal with a physical confrontation if needed, I'm certain the amount of unnecessary shootings would decrease significantly.