I applaud you on your efforts to really dissect the study in an objective way and point out all its flaws on a case by case basis. You are proving yourself to be quite the intellectual here, a man of intellectual merit to the highest order. Your proper grammar only helps your case.
But I must disagree with your thorough, objective analysis that is in no way a case of you getting pissed off when reality says otherwise about your worldview because fundamentally, war is humans killing humans, and that does not go down well on the subconscious level, and most troops weren't at the front, while those that were were quickly rotated out, at least in the case of the Allies in both world wars
Ohh pls Marshalls findings have been more less been debunked since the late 80s. He was a journalist who was skilled with a pen and the sucked up to military professionals, now people refrain from taking to much credit from him.
The Men Against Fire isn't backed by the kind of research Marshall claimed and he never did explain or show on what data he made the "75%" claim. He pulled stuff out of his ass and was caught making stuff up.
And no during his After Action Interviews in WW2 nobody seems to have heard him ask the soldiers who had or hadn't fired their weapon.
http://strategicstudiesinstitute.army.mil/pubs/parameters/articles/03autumn/chambers.pdf