There’s a clear campaign against the mentally ill with the global rise of fascism. Lots of it shows up in anti homeless rhetoric, but you can see it in the MAHA and anti vaccination movements.
There’s no reason to use the word “r-tarded” to describe someone. As someone who’s worked with the intellectually challenged, it’s an insult to them to compare them with people who are willfully ignorant.
Languages evolve. It’s a very common thing for descriptors of negative things to become slang for insults. Not to say we should be encouraging this behavior, but rather that policing it is ineffective at best.
Effective solutions address the underlying issues
(Destigmatization of ailments is a good thing, but doing so by stigmatizing the words themselves often has a Streisand effect)