Molotov-Ribbentrop is a great example of liberals not being able to think for themselves. Hitler literally wrote in Mein Kampf that his goal was to destroy the communist movement, occupy Russia, and enslave the Slavs. It is literally impossible for the Soviets to believe they could form an alliance, which means your conclusion that Molotov-Ribbentrop constitutes meaningful collaboration is incorrect.

If you study the history around it, the USSR wanted absolutely nothing to do with war after its revolution because it wanted to focus all of its efforts on building a new nation. The treaty was negotiated in attempt to delay armed conflict as much as possible and to take advantage of contradictions in capitalism/fascism to create that extra time.