I think my feelings on the matter are probably mostly in agreement with a lot of those I’ve seen on the Cannonfire and earlier Empyrean threads. Basically, an opposed pair of stats is fine for a personality or morality pair of stats, as long as those stats are truly opposed (at least for the purposes of the game).
A second point is that I feel such stats should generally be used for flavour text, not for success vs failure. Example: a “selfish” character might feel contempt for the struggles of others, but they should be just as capable of helping people as a “selfless” character. Sure, a selfish character would probably not help for nothing, but maybe they believe that they’ll be rewarded; likewise a selfless character may choose not to help for completely unselfish reasons. The only times it should be used as a success vs failure would either relate to mind reading (or similar), or potentially due to NPC reactions if the MC is famed for their selfishness/selflessness.
Finally, there should also not just be a cut-off at 50, but rather a band of grey (maybe 40–60?), over which the character is balanced between the two (again, almost purely for flavour text purposes).
That said, I feel that there can be exceptions to this, for example in the WIP Through Broken Lenses by @Interestedparty, in which (for example), “combat” is paired off against “friendliness”. This works because of the style of the game, which is all about trying to find a balance between being an amoral killer with no friends and a social butterfly who can’t protect the friends they now have.