All I can tell you is that one of the Brigades I worked with in Afghanistan did nearly a dozen 15-6s on civilians killed by soldiers. While all of them were ‘bad killings’ - the civilian was not trying to hurt anyone - all of the investigations concluded the civilian had acted suspiciously and the soldier acted within the ROE.
On the other hand, the Army started an investigation into another service’s action...the other service objected when it became obvious there were, shall we say, inconsistencies with the ROE.
In the latter case, I’m convinced someone should have been punished, since it seemed obvious to me that the unit screwed up.
I also have a son-in-law who left the Marines in part because he didn’t believe they would back him up if he found himself facing bad guys hiding behind women and children - which had happened to him multiple times in Iraq.
As you say, this is a very tough issue. I wish I knew what the right answer is.
I don’t believe in killing civilians. Moreover, its counterproductive in a counterinsurgency. But, many civilians take sides, sometimes both sides. I do recall watching a mother and her small child setting a booby trap. I had them both in my sights and wanted to kill them both. I didn’t. I do know that if I had, there would not have been an investigation.