I didn't write the following, but I think it is an excellent summary as to why it should be the position of Marxists and leftists in general to critically support Russia specifically with respect to the SMO. It was a response to someone saying they just didn't like the war in general and that it's just one capitalist state fighting a proxy war against another, similar to what you're saying. While it's understandable to feel that way, it is not materialist and it is failing to see the bigger picture. At the very least, I just think it's something you might consider. The person who wrote that response is @SimulatedLiberalism@hexbear.net, but they're apparently gone now or maybe using a new name.

and this struggle is between two capitalist empires which both want to do more capitalism, so there's no benefit to either side winning

I keep seeing this take cropping up in online Western leftist circle and to be very honest, I always consider this to be the laziest takes on war for people claiming to be on the left.

This is no different than saying that there is no difference for the left when it comes to whether the North or the South wins in the American Civil War because neither of them was socialist. Well, would it surprise you that Marx wrote an entire collection of essays just on analyzing the American Civil War?

To quote Lenin from his Lecture on “The Proletariat and the War”, October 1 (14), 1914:

For a Marxist clarifying the nature of the war is a necessary preliminary for deciding the question of his attitude to it. But for such a clarification it is essential, first and foremost, to establish the objective conditions and concrete circumstances of the war in question. It is necessary to consider the war in the historical environment in which it is taking place, only then can one determine one’s attitude to it. Otherwise, the resulting interpretation will be not materialist but eclectic.

Depending on the historical circumstances, the relationship of classes, etc., the attitude to war must be different at different times. It is absurd once and for all to renounce participation in war in principle. On the other hand, it is also absurd to divide wars into defensive and aggressive. In 1848, Marx hated Russia, because at that time democracy in Germany could not win out and develop, or unite the country into a single national whole, so long as the reactionary hand of backward Russia hung heavy over her.

In order to clarify one’s attitude to the present war, one must understand how it differs from previous wars, and what its peculiar features are.

We can write entire essays about the war in Ukraine, and it is anything but “a war between American and Russian capitalists”.

For one, if this is about Russia expanding its capital, why is the Russian Central Bank doing everything it can (including rate hikes and devaluing the ruble) to undermine Putin’s effort to achieve economic self-sufficiency in the face of unprecedented sanctions, and directly aiding the Western imperialist cause? If anything, it is stifling the expansion of Russian capital.

Such narrative crumbles at the slightest inspection of what is actually going on within the Russian political and economic structures, and points to a more fundamental division that Michael Hudson had pointed out regarding the conflict between finance vs industrial capitalism.

And we’re not even getting to the wider geopolitical implications of the war in Ukraine yet - what does it mean for Western imperialism? The anti-colonial struggles of the Global South? The effects on global financial institutions (IMF, World Bank, WTO) and the efforts to decouple from such oppressive structures (which is what de-dollarization is all about).

We have to ask ourselves, what would a fascist victory in Ukraine mean for left wing movements in Eastern Europe? What could the total subjugation of Russia - a country that has large scale military equipments, raw resources and minerals, and agricultural products - to Western capital mean for the anti-colonial movements in the Global South?

Leftists who refuse to apply a materialist and historical method to understand the world’s events will inevitably fail to see the underlying currents of the global state of events, and as such they cannot predict where the world is heading and will not be able to position themselves to take advantage of the impending crisis.

After all, it was WWI that resulted in an explosion of socialist movements within the imperialist European states, why? Because the socialists back then actually combined theory and practice (what Gramsci referred to as praxis) to take advantage of the predicament.