Marx didn't want the type of equality that would 'level' all difference. He is clear about that. And his critique of capitalism certainly sprouts from his vision of the despair that results from having one group of people (the capitalists) have such an unequal amount of power over another group of people (the proletariat). After all, the essence of Marxism is 'democracy in the workplace', so it indeed retains, in some sense, Bentham's egalitarian dictum that each person count as one person. But Marx was first and foremost a critic. He doesn't and can't say much about what communism would be like. It does indeed have something to do with equality. 'From each according to his ability, to each according to his need' is about as specific as he gets. He's searching after a sophisticated equality that can't be abstractly decided before the determinate situation comes on the scene, so communism can't be reduced to 'equality' because 'equality' can't quite capture everything Marx is wanting to say about communism. He wants a contextual equality, but that concept alone doesn't say enough, because you need the actual context to give the concept any kind of substance.