I remember Gygax said something like that (1 INT = 10 IQ) in one of the old books or articles.
The OP seems to be saying that if you ever portray a comically stupid character in a game of make-believe, that it's going to permanently harm someone, and then proceeds to repeat a scolding "ableist" mantra. He also wants people to police their language to never say the words "stupid" or "smart", because it apparently do irreparable damage to someone just by hearing the word. I think this is catastrophic thinking, which stultifies creativity, and renders people incapable of being resilient. After all, there are lot of things you'll encounter in life far worse than hearing a word, and you can't control when you have to deal with them.
This also sounds an awful lot like censoring comedy or fiction for "punching down", adhering to an oppression matrix world-view without considering context or complexity, and that's what I'm criticizing.
I could see some serious problems with this as a DM, say if you portrayed a stupid Ogre that the PCs have a chance to outwit, or a mindless gelatinous cube. Surely there are creatures in a fantasy game that actually are well...stupid.