There is no ambiguity, no argument possible about the ideology of Nazism and how it translates to action. We know how it went, what the founders of that ideology did when they got power.
There is a lot open about how Marxism translates to action. Indeed it is even proverbial how much the left has always been split between many different and opposed parties, each with its different programme on how to replace capitalism with some kind of socialist system.
One is unambiguously and absolutely evil, as demonstrated by its very founders. The other is a political ideology like many others, very open to interpretation both historically and in the future.
I don't care how it is 'interpreted,' I care what communists do when they achieve power.