So trying to argue the 0th pillar "freedom of use" is about specific software capabilities is mistaken. It's a gateway to the un-reconcilable "well N users demand my software have feature X, and an equal number also demand an incompatible feature Y." How could one ever satisfy the 0th pillar under this condition, and why would RMS never discuss this situation?

Perhaps because it is the wrong interpretation. :) RMS spends time at the "licensing level", not at the "what does your software do exactly" level.