I think what's hard to understand, at least for me, is how anyone believes a discussion of this sort is going to change how anyone actually REACTS in such a circumstance.
Regardless of the law, I fear for me life, I shoot. I don't fear, I don't shoot. Anything else is nonsensical.
I think I can say with confidence that just about every self defense school, LE agency and military organization disagrees with you. Training absolutely DOES change how and when a person will react. For me, thinking about what type of situation will cause me to use deadly force is just as much a type of training as my time spent on the range.
With all respect, you are wrong about this one. Grab a copy of Massad Ayoob's "In the Gravest Extreme" and read the chapter on fear as justification. It's a real eye opener.