Ignoring the genocides and the gulags for a minute, let's simply explore your theory that the USA and USSR were morally equivalent. The USSR conquered and imposed brutal slavery on every eastern european nation. The USA did not conquer any of the western european nations. We didn't even conquer Cuba. If we had the military power, why wouldn't we?
>your theory that the USA and USSR were morally equivalent.
mid-20th century significant share (if not half) of the world population was enchanted with the ideas of socialism/communism with those ideas symbolizing justice and freedom (not mass oppression as it ultimately turned to be). In that respect, _back then_, they were morally equivalent or at least close to it. We know better _now_, after observing of many decades of that failed experiments.
>The USSR conquered and imposed brutal slavery on every eastern european nation. The USA did not conquer any of the western european nations.
They all had their respective zones of occupation in Europe, Korea, Japan after the WWII. With time socialist regime in USSR zone turned to be the regime of "conquest and slavery", while capitalism in the western zones, South Korea and Japan happened to be more freedom conducting. For example South Korea wasn't fan of being occupied by US (for example among others http://en.wikipedia.org/wiki/Autumn_Uprising_of_1946 ) and it took decades for it to ultimately start benefiting from having been occupied by US instead of USSR. Again, back then, it wasn't that clear for huge number of people, and it took decades for the differences to appear clearly.
>We didn't even conquer Cuba. If we had the military power, why wouldn't we?
you think it is easier to fight in Cuba jungles than in Vietnam one or that Cubans would be less fierce fighters than Vietnamese?