The old standard test for a real c.o. was to ask them if they were willing to be reassigned to the Medical Service Corps, or the equivalent.
A real c.o. would usually be willing to be transferred from combat arms to a still “at risk” position where their life might still be endangered, but they would not be inclined to kill someone else. Carrying a stretcher in combat is not for the lily-livered.
If they refused MSC, then there was still the “out” of a psychiatric examination. This would look both for PTSD, and any pre-existing mental condition where they looked fine until put under pressure, then collapsed. Both of these are legitimate reasons for not sending them anywhere near combat, and they may no longer even be suitable for remaining in uniform.
Last, but not least, there are the rare individuals who have real problems unrelated to combat itself, and saw declaring themselves a c.o. as a way out of those problems. For example, a soldier who is being unfairly persecuted in his unit, or one who has severe family problems at home, but has been denied compassionate leave.
Then again, there are cowards. An unabashed coward is pretty worthless in combat, but still needs to be punished for the good of the morale of those who do their duty. The arrogant or stubborn coward is the kind that curses his duty and his country, aligns with the enemy and those opposed to the war effort, and is otherwise a scoundrel.
These are the ones that most need punishment, and gleeful punishment at that. They’ve earned it.
I was going to make a comment mentioning John F'n Kerry's name.
But that would be unkind to the honorable Sinator.