From what I understand, the core ideas of Marxism - the ones about epistemiology, metaphysics, sociology and history - are more or less universally accepted in those fields (to the point that a student of, say, history may learn Marx's theories as revealed truth, without even questioning them). His writings on economics are controversial, but again the core of it has remained largely unchanged.

Also, Marx thought of sociology, economics and so on as sciences, meaning that a theory is either right or wrong (or partially right). How many people believe in them has no effect on their truth value. So I don't get what you mean by an 'ideology that is friendly to a large part of the population or marginalized groups'.