The Left does this to keep you off balance. At any given time, the “acceptable” language for anything can become a sign of incipient, if not outright racism, sexism, or some other “ism”.
They utilize their “control” of language (via media control, education, and government fiat) to set the tone. At any time they have a ready-made tar to spread on people they disagree with.
There is another reason also.
Stigma.
The language changes when the subject has stigm
Witness the changes from idiot to retarded to delayed.