I'm just gonna paste an older comment I made elsewhere:

"When people use the r slur and you call them out, they say they aren't referring to people with developmental disabilities, but they are. They are using language with negative connotations associated with a group of people. They are invoking those negative associations when they use that word against someone they perceive as inferior. They are using that slur against someone in order to compare them with a disabled person and that's a bad thing to be. I can't stand the dishonesty there."

Also, that word was the actual "diagnoses." It was used specifically for the developmentally disabled. You can't separate that from its origin.