RMS actually did ask a few of the universities who granted him doctorates, if it was acceptable for him to use the title "Doctor". Some said no, some said yes, and some said he should use "Dr.(h.c.)"[0] (as in "doctor, honoris causa", where we get the term "honorary doctorate", even though, as RMS points out, it'd be perhaps more accurate to call it "doctorate for honor"[1]).

Of course, he took that as license to just do whatever he wanted to do. Personally I wouldn't even consider adopting any kind of title in the first place, but if I was of that bent, I would at least have the decency to append the "(h.c.)".

I do believe that RMS's contributions to the world have been significant, but, to me, at least, a doctorate is something you get after completing a doctoral program. If you don't do that, you should call yourself a "doctor, honoris causa" -- because that's what you are! -- not a "doctor".

But what do I know, I only completed a bachelor's degree, and even then only barely.

[0] https://stallman.org/articles/dr-stallman.html

[1] I learned something new today!