Doesn't this say more about the morals of America vs Russia than anything else?
Russians knew Americans would never do that to them, but Americans did not. (It doesn't matter if Russians would or would not, that's how they were viewed.)
I'm not sure what you mean by "morals". If you're implying that Russian knew that the US would never attack, but the Americans couldn't trust that the Russians would never attack, then that would still be propaganda at work.
If some Americans actually believed that the Russians were so maniacal that they would attack, even in spite of Mutual Assured Destruction, then those Americans were foolishly suckered in by propaganda.
Russians knew Americans would never do that to them, but Americans did not. (It doesn't matter if Russians would or would not, that's how they were viewed.)