Greg:
No offence taken.
You say that "Primitive Communism as a theoretical concept, though informed by "anthropological" observations actually derives from a deduction based on modern society." Why should we think that modern society can tell us _anything_ about prehistoric societies? And what difference would it make?
This suggests to me the positivism that seeped into the thought of some historical materialists after Marx's death, resulting in at least one grievous burden: mechanistic models of historical development, without a regard for logic or evidence. The positivist influence on Engels has been alleged, although I don't know of any conclusive evidence for this. I do know that Marx held Comte in low regard. I doubt also that Marx would have been enthusiastic about Engels' *Origins of the Family, Private Property and the State* (1886), had he lived to read it.
What is clear is that Engels was far more enthusiastic about primitive communism than was Marx: the 1st ed of the *Communist Manifesto* (1848) opens with: "the history of all hitherto existing societies is the history of class struggles". Note that "all". This was footnoted by Engels in 1888 with the words "That is all _written_ history". He then goes on to discuss "primitive communistic" land ownership in agricultural societies, apparently assuming "village communities" to be the original form of society in Russia, Germany, India and Ireland --- an idea which I don't believe is borne out by later anthropology, let alone by logic. Engels was still operating in the post Rousseau intellectual milieu of "noble savages" etc; his sources were flawed, especially since --- like most of his peers in anthropology --- he rarely did field work.
"The error in this criticism is that it tumbles over what is a significant part of the intellectual armoury of Historical Materialism..." Sorry, but I simply don't see "primitive communism" as being in any way "significant", or a useful weapon for historical materialists --- among whom I count myself -- - especially since it has not been shown conclusively to have existed. I don't think that's "a minor reason".
Regards,
Grant.