Jim, I've taken said "licensed qualified handgun courses' and 'hunter safety courses', and shot target for many years. I shoot weekly but haven't hunted in 20 years.
41 states now have a "CCL" (concealed carry license) and to get that license, one must go through a battery of background checks, get double finger printed, take a written test, qualify with 50 shot range test, go through 10-15 hours of classroom work, and pay about $260 for all this. "Non violent conflict resolution" is drilled into license candidates heads, all through the class room study. We learn about 'options', the gun being the last big equalizer.
"Situational awareness" is a big part of the classroom work. It boils down to "deadly force may be used if you fear for your life". And, we don't shoot to kill, we shoot to 'stop'. Shooter training is "center of mass", again, to 'stop'.
The first Texas CCL death happened in Dallas when two motorists bumped mirrors in tight traffic. The shooter was a frail guy, trapped in his car buy a very large, out of control guy, who tried to pull frail guy through his car window. Frail guy got to his weapon and stopped the big guy, who happened to die in the conflict. Turned out, big guy had multiple assault arrests and mental issues. Frail guy was 'no-billed' by the Grand Jury.
Had the tables been turned and frail guy attacked big guy, big guy would now be in jail for manslaughter, had he used his gun in the conflict. The situation matters.
So, to 'stop' another human with deadly force, you must be 100% at the end of your rope, no other options. You are not a policeman, superman, hero guy, or self appointed public guardian. Self defence, period. Third party deadly force is allowed IF life is in jeopardy, again defence. Texas adopted the "Castle Doctrine" where deadly force can be used for theft, at your home. Most folks would rather get new stuff with insurance money, then take a life. You may now carry a concealed handgun in your car in Texas, no license needed.
Between 1995 and 2004, handgun murders in Texas dropped by 18 percent. I think what's happened is that people are being trained, finally. You could call the CCL program a "well organized militia" and because of that training, some people don't carry at all and realize a gun does them no good, however, they come away licensed and trained. Criminals realize that....hey, that guy might have a gun in that car I'm about to carjack. The mere presence of a weapon can change anyone's attitude, 180 degrees, no shots fired. A CCL holder is bound to call 911 if he/she is forced to brandish their weapon to thwart a conflict, and any/all shots must be accounted for, should the weapon be fired.

So, to sum up, if you truly fear for your life, deadly force is justifiable. The courts will get the last say, and you will face them.