Are you an academic?
Usually your sort of poor judgement is found in people who live sheltered lives.
That killing took place in the middle of urban combat in Saigon during the Tet Offensive. Combatants don’t get arrested, they get shot. Combatants purposely not wearing uniforms get executed. We did exactly that in WWII with German soldiers in the US.
I am not an academic, I am a retired engineer/engineering manager.
As such I am accustomed to making dispassionate analyses - in my world of building and running complex systems (me and my colleagues were very much of the the tribe of “those that do”) this is essential.
This is a case of a passionate reaction. In my professional world that must be avoided like the plague. It gets in the way of trouble-shooting, design and implementation of solutions. And vastly more so in an emergency.
Kiplings poem “IF” is the core of us -
https://www.poetryfoundation.org/poems/46473/if-—