It was partly naivety but it was mostly treason. Communists had infiltrated the U.S. government and for many their loyalties were not to the United States but to the Communist Party and the Soviet Union.
As for feeling guilty about the Russians bearing the most brutal brunt of WWII the Russian people suffered far more when the NYT was regularly writing stories about how happy the people were under the starvation and slaughter of the Communists.
The people who bore the most brutal brunt of the war were not the Russian people but the Polish people. Read about the battle of Warsaw and how the Soviet Army sat back and watched the Polish resistance fight the Germans. Poland suffered by far the most casualties proportionate to their population.
Even if the Soviet Union had signed another agreement with Germany late in the war, the allies still would have easily defeated Germany. The German cities were being bombed day and night, German industry was destroyed and the German Army was short on supplies and close to starvation.
The German’s “ready” acceptance of Hitler has always been an issue not well addressed. Germany had experienced post WWl hyperinflation and now was well into the world wide depression. Hitler promised and delivered prosperity. In addition Stalin was starving the Kulaks in the Ukraine. The Kulaks were ethnic German farmers who had settled there under the reign of Catherine the Great. The Kulaks were still corresponding with their relatives living in Germany. Thus the Germans knew what Communism entailed and wanted no part of it. Hitler’s belligerent “anti-communism” was thus something they would tend to welcome.