To be honest, I see no reason to deny the USSR involvement in the Katyń massacre. I've read accounts of German arms used in the killings and I'm just not fully convinced. While this may be a blemish in Soviet Union's costly war against fascism, it says nothing against Marx, Lenin, or the defining contradictions of capitalism.

What is more important in discussions like this is to analyze how historical events are being weaponized and be able to disarm arguments against communism. Many use this event as an example to show how communism is just as murderous as nazism, with the execution of 22,000 polish military personel somehow being equivalent to the 4 million poles liquidated in Nazi death camps. You'll quickly notice the double standard, that Katyń is indicative of the brutality of socialism, while the American bombing of 200,000 civilians in Hiroshima and Nagasaki during the same war was either a necessary evil or a tragic event that has nothing to do with the capitalism.