Some people keep grinding this out like they know what they’re talking about, but I dare anyone to say what they want in its place. ‘Call a spade a spade’? Well, say it in the right place and see what the reaction is.
I’ve heard a slightly different version of its origin recently but prefer the one I first read, that it was a put-down by reactionaries to attempts by students at the University of California to stop people using racist language freely as if it were protected under ‘freedom of speech’. As far as I’m concerned it wasn’t, or shouldn’t have been, intended to ‘purify’ the language but rather a consciousness-raising way of realising who you’re insulting and the effect it has on them. If you still think it’s OK to use an old term for people of colour then say it out loud, or try the phrase “All Muslims are ..”, in a situation where you’re outnumbered by members those different groups. See how brave you are.
No-one is saying you can’t be critical of someone of a different ethnicity or religion or ideology, just be careful you’re not ‘tarring everyone with the same brush’, to use another old racist phrase. It’s not just impolite or bad for your health, it’s untrue.