But under highly adverse circumstances such as existed around May-July 1942, there was a widespread feeling that the outcome could be worse--total defeat, or an inability to claw any territory back. In any event Stalin, like Hitler, Nasser and Saddam, had such a good grip on power he could survive serious setbacks and humiliations.
His own military was mostly Shi'a. Or do you think less than 20% of the population controlled the Iraqi Army too?
There is a reason the Republican Guard existed. They were the only loyal ones, and they were the best equipped. They not only put down the civilian revolts, they also kept the rest of the military in check.
They left Poland and Czechoslovakia to the Communists in real life. It wasn't exactly a dignified move, but it was more acceptable than leaving them to the Nazis since the Communists were our WWII allies (and endured absolutely massive casualties in WWII) while the Nazis were our WWII enemies.
Czechoslovakia had already been left to the Nazis in real life once in 1938 and then later to the Communists - so they were abandoned twice. The Allied response to German's invasion of Poland was not exactly strong either and if Germany had never attacked anyone else, but just sat there was well, it would in my opinion eventually have defused and ended the war. Germany just called their bluff when invading Poland, but the West had no desire to actually fight at that point yet.