I’m not sure that failure to imagine how evil, or ill, Putin was constitutes leading Ukraine down a primrose path to war.
And if Ukraine had not gone about failing to implement the Minsk ceasefire agreements, and blathering about becoming a member of NATO, it would not have invited Russia to visit an attitude adjustment upon them. Russia's doctrine toward Ukraine was as clear as the USA Monroe/Polk doctrine caliming two continents.
Beyond the issue of right and wrong, there is the issue of poking the bear when the bear is the biggest, baddest SOB in the valley and can kick your ass. Relying on others to put boots on the ground to fight your war is not a wise choice if it involves Russia and an unwinnable war. Nobody was obligated and nobody volunteered for that one.
Nobody had to imagine that Putin would do what he considered necessary. That's like putting missiles in Cuba and being surprised that the reaction was a naval blockade (an international act of war) and a threat to carry forward to a nuclear war if needed. That was not considered evil or ill when we did it.
JFK was reacting to Russia putting nukes 90 miles from our shores. I don’t recall that there was any suggestion of putting nukes in Ukraine, especially since they had voluntarily given up the ones they had. UK and France have nukes. How many other NATO members have hem set up and aimed at Russia, 90 miles away at that? This was a blatant invasion attempting to take over all of Ukraine and its resource riches in the east. Since the total takeover failed, east Ukraine is Putin’s fall back position. His multi months deployment of large numbers of troops all around Ukraine’s eastern perimeter was a blatant provocation, and very hard to ignore without looking like wimps. I doubt there is anything that could have stopped Putin short of nuclear threats by the west.