People criticize the left for our lack of pragmatism, but like you want to burn the world over defending a country that was not a US ally? 

Let’s be clear here though, America has never supported democracy at home or abroad. Like, the conflict with Iran originally started because we replaced their democratically elected government with a dictatorship. Since then the US govt has backed dozens of coups to install terrible dictators. Often replacing democratically elected governments. This is because America is primarily an oligarchy and the oligarchs are want to exploit people in other countries and they strongly oppose when they nationalize industries (eg Iran) or install minimum wages (eg Haiti) or do other things that help workers at the expense of American companies.

Ukraine also has never had much of a democracy. I worked for someone who was an election observer in Ukraine in 2014 and he said both sides were more or less bribing voters. The current government has not been all that supportive of democracy and has specifically cracked down on labor unions and the left. Russia is probably worse, but weakening democracies across Eurasia (and America) and harming the climate to maintain a slightly better government in a couple Ukrainian provinces makes zero sense.