The reason I mentioned Trotsky is because no one better symbolizes the fact that you are WRONG when you say 'Marxism led to Stalin'.
Trotsky---indeed all of the Bolsheviks---died for what they believed in.
Guess what that was?
Probably the same things that the Nazis died for: personal ambition, power, some ridiculous and contrived ideological fairy-tales, etc. Most died because they couldn't be troubled to think for themselves, and allowed some self appointed 'expert' to decide their lives for them. For a large proportion of the rest, like the Cheka, or the SS camp guards, or the Eisenstruppen, or the NKVD, they were sadists who didn't know when the jig was up.
Crude comparisons between Nazi Germany and Stalinist Russia fails to recognize my statement above: that the original Bolsheviks---representing the humanist ideology of Marx and Engels---were slaughtered by Stalin to prevent Marxism from flourishing in the U.S.S.R.
Criticizing Stalin in no way repudiates Marxism. Quite the opposite.
But it's a great scare tactic for the ignorant, isn't it?