It's a valid hypothesis and a model that works. Meaning, it has no internal inconsistencies, no glaring logical fallacies, and it isn't based on wildly arbitrary assumptions (in stark contrast with, say, The White Goddess). The political affiliation is indisputable, but "agenda"? As far as I know, no one believes that it compromised his scientific integrity - he didn't fabricate evidence or anything. His anthropological model isn't a gospel (nothing is, in science), but it's a very useful paradigm to have in mind, IMO.
*shrug the second*