In my humble opinion, this is nothing like the Molotov-Ribbentrop. Molotov-Ribbentrop gets a lot of bad advertising due to cold war propaganda, but even western leaders in the west at the time like Churchill admitted that the Soviets had no other option (if you want evidence I have plenty of reference, feel free to ask :)

The Soviets spent the entire 30s warning of fascism and trying to build mutual defense agreements with France, England and Poland and they refused systematically, even when in 1939 the Soviets offered to send 1 million troops together with artillery, tanks and planes, to the Polish and French borders on exchange for a mutual defense agreement, but the French and English ambassadors received orders not to engage in actual negotiations and just to postpone the agreement, since they wanted the Nazis to invade the Soviet Union.

Either way even if you fundamentally disagree with what I'm saying, what was the alternative? Poland was going to get steamrolled by the Nazis with or without the soviets controlling the eastern part of it (as proven by the fact that soviets started invading some weeks after the Nazis). What's more desirable, half of Poland having concentration camps, or the entirety of Poland having concentration camps?

All of this could have been prevented in my opinion if western countries agreed to engage the Nazis together with the Soviet union, as the soviets suggested as an alternative to the Munich agreements. So the lesson in my view is: to fight fascism, listen to socialists (who are the ones who actually defeated most Nazis in the eastern front)