Neutral/Evil alignment

[Unoriginal]

C) hiding among civilians, refusing to evacuate those civilians, or otherwise using them indirectly or directly as human shields is a big NO and reverts the responsibility. if your enemies are shooting from a house and there are civilians in that house, you can fire freely, and whatever happens to the civilians is the enemy's fault

A soldier who shoot a civilian who's being used as human shield is still held responsible/liable for shooting a civilian.

There's a reason why the enemies taking hostages can stall a military operation for a long time.

So I shouldn't see moving someone towards evil as a way to punish something that I as DM consider a misbehavior. It shouldn't be about 'would I have preferred if you acted differently, from an out-of-character viewpoint?'

I'm not sure about the rest of your post, but this part I agree with at 100%, and I think it is very important to underline it and explain it to the players if they don't get it.

A PC's alignment shifting toward evil isn't a punishment, nor is a PC's alignment shifting toward good a reward.

Alignments in 5e are descriptors for typical behavior, so a shift is just the description staying accurate to the shift in behavior or becoming more accurate.