I am not a member of the Royal Society, and although I do represent its patron, that doesn't seem like it should entitle me to a vote. But I did teach two actual full classes with full rosters of students, both of which were carried through to completion and from which students were able to matriculate: one on Hemingway and a seminar on wikimarkup. So hopefully this body will value my perspective.
Anyway, from what I can see, very few of the members of the Royal Society have been measuring up to the requirements of their positions. Fellows and Senior Fellows (including the President) are expected to deliver annual lectures to the Society that pertain to their scholarly interest. I can name perhaps one or two Fellows who have done this in any reasonable form. Fellows are also expected to produce a twice-yearly symposium, but I am not aware of one.
So perhaps I could suggest that postnominals only be offered to those Fellows who are in good standing, rather than those who wrote a short essay once, some years ago?