This kind of moralistic question is better suited for ethicists than straight historians, but I will try to provide some information for other side of the argument you are explaining.

A lot of my experience comes from the early postwar era and the early Cold War between the United States and the Soviet Union. Certainly, Stalin had perpetrated a stunningly large series of purges in the 1930s that eliminated anyone who could potentially be called a political dissident. These purges spread fear through most urban centers. It is unclear to today how much Stalin knew about the specifics of these purges. He certainly sanctioned the larger initiatives, but there is an argument to be made that lower-level bureaucrats were responsible for perpetrating the more egregious abuses. Regardless, Stalin's purges and the forced collectivization of agriculture which led to famines across the USSR from 1932-33 were responsible for millions of deaths.

In World War II, however, the story changes. Certainly Stalin aligned with Hitler in the Molotov-Ribbentrop Pact which secured the Soviet Union an eastern partition of Poland. It is important to note that Stalin warned Great Britain and France about German aggression and offered to form a military alliance with them in expectation of Nazi expansionism. When these plans fell through, Stalin aligned with Germany in an effort to avoid becoming the target of their aggression.

During World War II, the Russians suffered as many as 20 million casualties as they absorbed the full force of the German army in Operation Barbarossa. Stalin pleaded with Churchill and Roosevelt to open a second front in Europe. Their promises of a second front were delayed year after year until in 1944, when the USSR had begun turning back the German invasion.

The USSR did perpetrate atrocities during the war. The Katyn Massacre of innocent Poles and the mass rape that followed the Red Army were certainly unforgivable, but again there are questions as to how much top government in the USSR is to blame. There is evidence that they perpetrated cover-ups or showed an unwillingness to get ahead of these potential issues, but further details are often hard to find.

After the War, Stalin pursued a buffer zone for the Soviet Union. His primary interests were to ensure that Germany would be "pastoralized" or incapable of industrial rearmament necessary for another war. Eastern Europe would also have to be made into friendly territory to ensure Germany could no longer find an easy runway in the plains of Poland in their run-up to another Soviet invasion. After being invaded by Germany twice in as many decades, Stalin wanted security for his country, which is understandable. Whether or not it was moral to remove some freedom of choice for the Eastern Europeans is more unclear. It is important to remember that Churchill and Roosevelt basically ceded a Soviet sphere to him at Yalta. Stalin was initially willing to reconcile the Lublin and London Poles into a government in Poland that was not wholly a Soviet puppet and contained opposition. Additionally, he allowed the West to have a free hand in creating conservative, friendly democracies in France, Italy, and elsewhere.

Truman, however, was unwilling to pastoralize Germany. In part this was due to information from Dean Acheson and Paul Nitze on ensuring that Europe be rebuilt, including Germany, to ensure the global economy functioned to America's economic advantage. This caused talks to break down as Truman began to change his mind on the Yalta Conference. Stalin became so desperate to reopen talks, that he even offered the reintegrate Germany and cede the Soviet Zone of East Germany in his "Stalin Note" in exchange for some semblance of reassurance from the West that Germany would be nonaggressive to Russia. This Note and future efforts in the Soviet "peace offensive" were rejected.

I could go into much more detail, but I will wait to answer questions. It is certainly true that the USSR put down rebellions in East Germany and Hungary with startling brutality, but it is also true that a majority of people in East Germany who lived under the GDR remember as mostly or completely better than life today. Many Russians feel the same after the humiliation they suffered in the 1990s. These facts bring a complex, nuanced view of Soviet morality to bear. I hope that was helpful.

Sources:

The Soviet Experiment by Ronald Grigor Suny

NSC 68 and the Origins of the Cold War by Curt Cardwell

Stalin's Wars by Geoffrey Roberts

Drawing the Line by Carolyn Eisenberg

Present at the Creation by Dean Acheson