I agree with Carl on this one, in a particular sense: Martin Heidegger, without intending any form of insult, wrote "Science does not think". The sort of problems that predominate Marx's area of interest are not reducible to a science, and requires thinking. IMHO, moral reasoning is the highest form of that kind of thought. Now I know very little about Marx (though the little I have read of him presents a deeply moral philosopher quite different from the individualist prophet presented by the faithful), but if he indeed made significant contributions to this area, he would have had to transcend science.
--ravi
P.S: I must say of Carl's writing on the list that when evaluating it, one needs to remember (borrowing from Nietzsche): whatever is written with such style and wit lies beyond right and wrong! ;-) I suspect its not a coincidence that Karl [Marx], Carrol and Carl share a great similarity [not just] in names! ;-)