They held no moral high ground; plenty of those 20 million died fighting for the Axis (Ukrainians welcomed the Nazis as liberators, and that only went sour when Soviets slipped behind the lines to sabotage that deal by spurring German reprisals against civilians - they admitted it after the wall came down). They had already invaded the Baltic states and half of Poland before Hitler attacked them (they had arranged those invasions/seizures with Hitler beforehand), and in the 1930s had already killed millions of their own people (hence the Ukrainian support for the Axis). Other countries with nothing but positive feelings towards the Western Allies participated in Operation Barbarossa because of Soviet threats to their freedom BEFORE the war; that is why resistance was so stiff even after it became clear the war was lost.
The Soviets held no moral high ground; we lowered our own image by supporting them - and Eastern Europeans in particular don’t mind saying so to this day.
I went to college in the ‘80s with a girl (Kathy) whose Ukrainian “baba” (grandmother) had the misfortune of living in both Soviet and later Nazi camps. She said the Nazis treated them better. In fact , one of the Nazis saved Kathy’s mother from drowning when she was very young.
Baba was one tough old woman. She was toothless, knew little English, and hoarded everything from old corn flakes boxes to pieces of string. Everyone loved her.
Ukrainians in German uniforms chased out remnants of the SS holding Prague and freed it handing it over to the Czech locals. Only to be turned over to the Commies and be subsequently executed.
However, it was the Nazi racial policies that turned much of that sympathy into hatred.
Another reason we kept giving the Soviets so much aid, was that Stalin kept threatening to drop out of the war and make a separate peace with Hitler. True, the Soviets were confronting most of the German Armed forces....however, it was because of Stalin's incompetency, the bungling yes-men that STalin replaced them with, and the time it took for competent majors and colonels to reach rank was the reason the Soviets lost so many men.
We faced the Japanese Empire pretty much alone, with a smaller percentage of our forces dedicated to fighting them (the bulk of our effort was to fight Hitler), and yet only lost 111,606 men in the nearly four years we fought there.
I do think we agree that the Soviet Union was the most evil nation of the 20th Century. The reasons the Nazis had to be stopped was because the Germans are much smarter people, and Hitler was a jackass.