Throughout history the legitimacy of violence has been a common debate. Was it right for one marauding tribe to go to war against another for more land or food or offspring? Was war to avenge an injustice OK? If so, when and at what level was violence excessive?
The ancient Romans believed in total war until their targets capitulated completely. Although the Christianization of the Roman Empire saw the rise of "just war" theory, religious wars in those days between various sects accusing the other of "heresy" almost nullified the righteousness of each sect's beliefs. Not long after, Islam adopted the pattern of conversion through mass capitulation under duress if necessary. And so it went, some wars were waged chivalrously and others visciously.
So despite "just war" theory's existence, it's utility waxed & waned over the centuries. America's Civil War might have been "civil" in that both sides strictly forbade violence against non-combatants, but the combatant death tolls were truly horrific. And from then on war's capacity to inflict horrific harm to lives and treasure has become boundless.
Enter a debate on the ethics of war - again.
Commonly, advanced democracies believe that violence between states or by governments on any sect among its population is wrong. Enter Putin. Clearly his fear that Russia's former Soviet satellites were aligning with NATO and the EU was a critically serious threat to Putin's idea of Russia's national interests. (Note, though, that Putin's kleptocracy defines Russia's interests as everything that keeps Putin rich and his kleptocrat lieutenants enriched and in power.) So, in cahoots with Russian Orthodox Patriarch Kiril, a long-time former KGB compatriot of Putin, Russians are told that Russia is saving ethnic Russians from Ukraine and stopping Western immorality from expanding into Russia's neighborhood. So does Russia's #1 religious leader Kiril endorse Russia's aerial on Ukraine's civilians? Does Kiril understand the concept of "proportionality' in war?
If Ukraine's response to Russia's violence on civilians were to be "proportional", then should bombardment by Russia on a Ukrainian city be matched by a Ukrainian bombardment of a Russian city? If this is a consideration, then Russia ought to make those air defense units very prominent. Two world wars showed Europe the horrors of matching violence with violence. But for how long should Russia's civilian population be allowed to remain dumb to the violence Russia's military has unleashed on their civilian counterparts in Ukraine?
Make Russians realize that their violence vs civilians has consequences. Somehow. How?