Communists and socialists defeated the Nazi's and were the vanguard for every major anti-racist, anti-sexist movement in every country throughout the 20th century, and still to this day.
Conflating all socialists with communists and all communists with Lenin, Stalin and their ideological heirs is questionable, but it depends which history of time you're talking about. Communists were actively helping the Nazis in 1939-1940. They gave huge quantities of raw materials to them when they needed it most, signed a non-aggression pact with both the Nazis and separately with Imperial Japan, they jointly invaded Poland with the Nazis, invaded or threatened to invade several countries in Eastern Europe in order to acquire territorial concessions, and instructed communist parties of the world to oppose the war against the Nazis. Which they diligently did despite the hardcore ideological whiplash it entailed. The USSR never matched it's egalitarian rhetoric, making hasty retreats on women's rights as soon as they realized they wanted to encourage population growth, never really trying to do anything about rampant racism against central Asians, Muslims and Siberian natives despite theoretically being opposed to racism, and of course their ongoing awkward relationship with the idea of non-totalitarian rule.
Communist parties around the world only regained some kind of moral high ground after they divorced themselves from the USSR, which they didn't really do until the Cold War kicked into full swing and even then they were engaged in frequent apologetics for the USSR. Socialist movements more broadly did have an often awkward relationship as "fellow travelers", but at least could distance themselves more easily from the atrocities of the USSR and more openly implement their policies inside the framework of a democratic system. It's a lot easier to say that the socialist movements were a strong positive force than it is to say that the Communist ones were.
Getting back on topic a bit though, a hammer-and-sickle is probably just as upsetting as a swastika for somebody living in the Baltic states, being as they were grievously mistreated by people flying both of those flags in sequential order. The fact that there were also euro-communist movements in the 70's that weren't Stalinist isn't really going to make that issue go away. Personally I'm in favour of including both symbols in my historically themed videogames, but I can also see a fair degree in asymmetry in the way that people want to sweep Nazi symbology under a rug, but are pretty happy to have all of these videogames starring Soviet soldiers flying the red flag and just not commenting on all the heinous shit they were doing before, during and after the Eastern front opened up or really caring that we're only 26 years removed from the period where a dozen or so states in Europe and Central Asia were living under the oppressive thumb of their regime.
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