This strikes me as essentially nonsense, in that it sets up an either/or both sides of which are nonsense. Of course society was "not based on some rational system" - what in the hell would that mean anyhow.
But neither does it make any sense to worry about "the originary ontoljogical domain of Man" - I am tempted to say that even Charles's mechanical biologism is more sensible than that. And whem we speak of a "manifestation of X" we mean that X has an independent existence of its own, which becomes palpable or graspable or intelligible only in respect to its "showing forth" in another guise. But Being is merely a label for anything and everything, a trick of language as it were, and the chase after it or its "manifestations" can only lead to nonsense.
To speak of society as based on "some rational system" is of course a vulgar idealism, a matter of taking the metaphor of a social contract too seriously and fantasizing a bunch of utter strangers coming together out of nowhere to sit down around a table and begin excogitating a contract by means of which they can form a society where none existed before. Why in the world would someone devote a lifetime to demonstrating the falsity of that. I wouldn't take Tahir's criticisms seriously (or even bother to read them through), but you and Dennis are beginnign to make Heidegger sound frivolous.
Carrol