Mostly I was trying to speak from my understanding of the anthropological evidence. But I also think you may be interpreting my use of the word "religion" in that post more narrowly than I intend. I was thinking about
Geertz' definition:
"As we are to deal with meaning, let us begin with a paradigm: viz., that sacred symbols function to synthesize a people's ethos—the tone, character, and quality of their life, its moral and aesthetic style and mood —and their world view—the picture they have of the way things in sheer actuality are, their most comprehensive ideas of order. In religious belief and practice a group's ethos is rendered intellectually reasonable by being shown to represent a way of life ideally adapted to the actual state of affairs the world view describes, while the world view is rendered emotionally convincing by being presented as an image of an actual state of affairs peculiarly well-arranged to accommodate such a way of life....
Let us, therefore, reduce our paradigm to a definition.... a religion is:
(1) a system of symbols which acts to (2) establish powerful, pervasive, and long-lasting moods and motivations in men by (3) formulating conceptions of a general order of existence and (4) clothing these conceptions with such an aura of factuality that (5) the moods and motivations seem uniquely realistic."
The strength of that definition is that it's
very general, i.e. it's not connected to any concept of the supernatural (but then, some versions of Buddhism are atheistic...). The weakness is also that it's
very general, so much so that it would even allow for secular religion. But when I said that I think religion is fundamental I mean that I think the social need to connect an
ethos with a
worldview as described by Geertz is fundamental, particularly to the legitimation of social institutions (on which see also the work of
Peter Berger).