These trade-offs are also the reason why more liberal Western societies are plagued by a new generation of social ills and inefficiencies. I happen to be an very liberal person but it's easy to see that people sometimes respond poorly to the absence of value or things to believe in, no matter what these values themselves might be.
Although the person you replied to did cite a medieval concept, it's still very much relevant in the modern world since we now have to deal with anomie on a large scale. I do hope the liberal modes of thought will prevail however! But if there were no trade-offs they would have won out a long time ago.
Yes, it's because we have tribal roots: we have spent 99% of our evolutionary lifetime in groups of countable quantities and competing with similar-sized groups.
> Clearly the fact that they are widespread instincts indicates [..] there is a trade-off at the societal level.
No, it merely indicates that there may have been a positive trade-off for this trait. Assuming that every trait is a net positive now or must have once been a net positive is a naturalistic fallacy.
> people sometimes respond poorly to the absence of value or things to believe in
Since there are narratives out there that do not paint artificial boundaries (and some do, but do not pursue confrontation because of it), this in no way excuses racism, jingoism, or nationalism.