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.
And then in a decade or two people will have started to use the word disabled with a derogatory meaning and we can no longer use that word either.
The same with “mentally challenged”
“Special needs”
It has already started. It will start immediately with whatever word they come up with to replace it. If someone is being particularly stupid, someone else will find the strongest word they can to insult them. This will never change.
Already happening, and already being railed against. You can read a great many arguments from certain communities that decry anyone calling them disabled or handicapped.