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!
So, regardless of your personal opinion, he is allowed to call himself Dr.
This is character assassination, leave it alone.
One of my professors used to talk about the difference between a Masters degree and a PhD:
"To get a Masters degree you have to learn something. To get a PhD the world has to learn something."
The world has learned a great deal from RMS. Regardless of what one thinks of him as a person, he's probably been more influential on how the world thinks about software than the vast majority of PhDs.