That's just redefining the meaning of the word 'belief'.

Ultimately, I know they don't believe anything they say, because they had to invent a word to describe the concept of 'doing things that align with that you believe in' - "praxis".

Nobody else on the face of the earth needs a word to describe this action, because it's just fucking implicit with the very concept of belief. People have words to describe the opposite - 'hypocrisy', a westerner would say. 'Shirk' a muslim would say.

But only the marxist has a word for living by beliefs he claims to hold. Only the marxist has need for such a word.