There is a view that "syncretism" used to be the "default" religious response and natural human tendency (well, why not maximize your portfolio and hedge your bets?), but that a minority of religions that explicitly defined themselves in opposition to other religions had huge evolutionary success, and some of them have shaped modernity.
Sorry I don't have anything useful to comment, but just wanted to thank you profusely for this post. I relate pretty strongly to these very problems, especially the uncertainty of usefulness (often the certainty of uselessness) and the opportunity cost considerations. I don't know any good article where someone talks about handling this issue.
Would love more commentary on how you seem to go from cooperation to altered state of consciousness, specifically, from (i) below to (ii) below:
(i) Your comment <blockquote>I live in a local pocket of the universe where even my interactions with complete strangers – such as the salespeople at stores – tend to be friendly and warm in tone, or at least politely neutral.</blockquote> This, I can and do believe, is a natural denouement of cooperation.
(ii) That bit about altered states of consciousness ("pure love"?). It is not clear to me that this has anything do with the cooperation you mentioned.
To begin with, the latter doesn't seem like something one grows into with increased "social intelligence", but rather "quantum jumps" that are taken at unpredictable moments that one cannot engineer. Secondly, it is not clear to me at all that people who integrate a greater understanding and dexterity with cooperation in their personal lives have any higher chances of reaching these altered states of consciousness.