Without NATO aid, Ukraine will just plainly be taken over by Purine Russia.

The war would end, a whole lot of people would stop getting killed, and it would open a sliver of space to organize on class lines instead of nationalist ones.

As it is, it is basically illegal to be a communist or an anarchist in Ukraine, and the country is under martial law with NATO-armed and trained fascist brigades doling out summary justice. Could it get worse? Why should the left advocate for people to die on the hill of a country which arrests communists, dismantles labor unions, and liquidates public infrastructure on internet auctions for foreign investors?

If you take the most vulgar Anarchist approach, all states are bad, full stop. Political practice doesn't even operate on that paradigm. You struggle to undermine oppressive hierarchical systems that you come in direct contact with through direct action. If you take the vulgar Leninist approach, the Proletariat should struggle for the overthrow of their Bourgeoisie (this would include the proletariat of Ukraine and Russia respectively, as well as the proletariat of Western countries which see this conflict only as a means to strengthen their military alliances and diplomatic positions). Of course, the situation is too nuanced to apply such a vulgar approach, but that should be the STARTING POINT for anybody who considers themselves anti-capitalists. You should be able to justify any deviation from those bedrock positions.