With reference to "stupid" and "idiot" - I also have some difficulty as seeing the use of them being as ableist as a number of other words. "Stupid" has, so far as I know, never been used in a medical context or as a diagnosis, and calling someone stupid isn't a comparison to people with intellectual disabilities. (I have never found or been directed a source indicating that stupid actually means anything more than "unthinking, dull, senseless, foolish, inane" - yes, it's an insult, and yes, it can be leveraged in a that implies that the person is inherently lesser, but intelligent people can behave in stupid ways, and "you are inherently less intelligent and therefore worthless (because people who aren't smart enough, or have difficulties are worthless)" isn't a necessary implication of the word, unlike "imbecile" or "retard".) "Idiot" I can understand more, because it *was* used in medical and legal contexts as part of the oppression of people with disabilities, but it's also a word with a long history of meaning foolish or incompetent that far, far predates that use. (I try to refrain from using it at the very least online because I know that people find it hurtful, but it's still one where it's not clear the the current usage's primary link is to the medical/legal usage.)

And no, nobody's personal experience should invalidate all other argument or evidence, and using it that was is generally in pursuit of shutting down an argument that is making people uncomfortable. Words are complicated, and so is their effect - as a normative force in society, as a specific force on an individual.