It's a long way from "Flat Tax Maybe Not Good" to "Proletariat, Seize the Means of Production Now!"
By your logic, Eisenhower's America was communist because income tax was much more progressive than today.
And if, just for the sake of argument, we suppose those were equivalent... Then the huge popular support for (1) means those who decry (2) are actually a weirdly out-of-touch political minority with delusions of being far bigger than they are.
Then we have a very different understanding. And yes the post war heist that destroyed long term economic common sense all over the western world turned into a permanent ongoing shakedown