On the one hand the demons are genocidal mass murders, on the other hand they've lost the battle and several of them have reverted to babies. Babies that have retained the memories and personalities from when they were murdering. Babies and women who fell in love with the demons. None of which have even said "sorry" about all the murdering.
I really want to know where the author is going with this. Just because the murdering bad guy turns himself into a little girl or a baby doesn't make the people they murdered not-dead. I'd argue the physical appearance of the demon genuinely doesn't matter, a baby, a pretty girl, a crystal, a tree;, all irrelevant, it's actions that matter.
I think it's more that
the demon lord specifically doesn't seem to have had the same effect happen to him, or maybe he's just an actual baby(?).
We don't even really know if the demon lord
has murdered anyone, since there's no evidence of that (unless I missed it), and the goddesses kinda just started the war for shits and giggles.
Also, another point would be that the people the goddesses are mad about dying are practically hitmen that they hired to wipe out the demon lord's army, so at the very least
the heroes that died were arguably killed in self defense.
Honestly, I don't remember well if/how the demons killed people (we're ~250 chapters in, after all), so
maybe the generals deserve it(?), but my points still stand.
The demon lord thing is not
super clear right now to my knowledge, but you get what I mean. Killing the immortal demons that retain memories isn't the point.