Human tragedy aside (and it absolutely is, no doubt about it, on all sides), it really depends on the context.
Striking the retreating army is the 'easiest' way to 'neutralize' it, Clausewitz writes about it, and I am sure it's been practiced for thousand(s?) of years before that.
For a timely comparison: would it be 'vindictive' when Ukraine strikes the retreating Russian army in the Kyiv area before they regroup and attack the Donbas? I don't think so. Seems like a good idea, actually.
Striking the retreating army is the 'easiest' way to 'neutralize' it, Clausewitz writes about it, and I am sure it's been practiced for thousand(s?) of years before that.
For a timely comparison: would it be 'vindictive' when Ukraine strikes the retreating Russian army in the Kyiv area before they regroup and attack the Donbas? I don't think so. Seems like a good idea, actually.