In Sociology, W.E.B. DuBois is cited as an example of a type of social scientist (just as Marx is often considered a founder of the Conflict Theory school in the same discipline). Based on the data he gathered, DuBois sought certain policy or cultural changes. Real scientists can't do that? (Marx laid his cards on the table and said the point wasn't just to analyze or intepret society, but to change it.)
The theory of surplus value and the theory of historical materialism are economic or at least social scientific theories. If the social sciences aren't really sciences -- and plenty of folks argue that -- then, yeah, Marx isn't a scientist. But neither is anyone working in any of the soft sciences, then. To say he isn't a scientist because data-gathering sucked in the 19th century - that'd wipe out a lot of scientists from that period, not just folks in the soft sciences.
-B.
Carl Remick wrote:
"Yes, but I think a lot of his research was hit-and-miss, based on his own inadequate resources and the primitive state of data gathering in the 19th century. [...] He isn't a a true scientist -- a detached neutral observer who is simply interested in how the system works, not in making normative judgments about it."