> - They grossly compromised their ethics by collaborating with the Nazis to invade Russia.
Be aware that good and evil are defined by the victors from the victors viewpoint. The Nazis were evil incarnate because they were the enemy, Uncle Joe was a good guy because he was attacked by Germany.
The truth is that they were both evil with Stalin being an order of magnitude worse than Hitler. With the notable exception of the Jews, most non-political Germans were not in fear of their lives from Hitler. On the other hand the story of Stalin's purges is almost beyond belief. I think it was Soshtykovich? that said that the war brought in good times because the purges stopped. (The purges killed far more than the war.)
Anyway, in that context, "collaborating with the Nazis" is purely a western point of view. The west did not help Finland one bit during the Winter war, and so it is a bit rough to criticize them for taking the only help that was on offer.
From the Finish point of view it looked like Germany would win so make hay while the sun shines. There was a movement in Finland for "a short border and a long piece", i.e. to push the border back into Russia where its length can be minimized. The Germans wanted the Fins to take Leningrad. But the Fins wisely did neither.
With the wisdom of hindsight, it would have probably been better for the Fins to wait and see. If Stalingrad had fallen there would then be plenty of time to push the soviets out of Finland.