We agree on the empirical fact that many people generate suffering for themselves by encouraging an inner narrative of complaint about others' behavour.

If there's disagreement, it seems to be about whether or not this is necessary. I contend (along with thousands of wise narrators from just about every culture throughout human history) that it is not. This is just spiritual/ideological/psychological pragmatism (depending on your metaphysical orientation), and is intrinsically unrelated to altruism or perhaps ethics. Indeed someone holding a view that judgement of others is ethically or morally 'bad' merely shifts the target of the wasted mental judging-activity to their own putative ego.