My realization and experience is that religion is not as simple as Marxism would have us believe. Marx was not really a researcher of religion, his understanding was stuck at the level of research already done by his predecessors.
To understand religion, one must go deep into it and practice it. Practice is the only criterion for testing the truth, and no one has the right to speak without practice. Sima Nan's exposé of qigong is so profound because he practiced it.
There is no right to speak without investigation, and there is no right to speak without practice before religion. This is the only way to study and explain religion. Because, religion is the study of life, and the key area of study is in spirituality, that is to say, religion is the study of ourselves, and if you don't practice it yourself, you can't understand yourself at all, and to deny it without understanding yourself is to be irresponsible to yourself.