The ultimate war erases all the rules of engagement, including treaties.
The West is civilized and relies on civilized instruments to maintain life and peace. Civilized instruments like treaties and trade agreements.
If your enemy is dead at the end of the war, there are no more rules, so why not fight to kill the enemy beyond any return to power?
If the enemy is still alive and viable at the end of the war and civilized instruments have survived to bring about justice, then what difference does it make? The civilized people will leverage justice and death will come anyway.
Putin will be ruthless without being hemmed in by civilization.
Civlized soldiers will think differently than their ruthless leader which creates the question, why did the Russians primarily strike residential areas and buildings? They are in violation of international law. Or. Are they warning everyone as to what was supposed to be coming?