And if so, why is one considered less acceptable than the other, especially on social media?

How many unsolicited letters from a CEO are you getting per day? How much leeway did secretaries generally have when talking dictation for correspondence?

no, for one thing people used to actually transcribe live from talking. if you delegate to a human, you assume humanlike qualities, especially for correspondence. would you go hang out and get a beer with current-gen AI?

social media is actually one place where I'd argue nobody gives a shit what ANYBODY writes.