And how do the "language moves on" people feel about "mong" and "spaz"?
Those are different. They were used as medical terms until very recently - I’m relatively young and still remember The Spastic Society before it changed its name. Mong was definitely used as a derogatory insult meaning ‘like a Down Syndrome person’ when I was school-aged. Idiot and moron were certainly of a much older generation meaning ‘medical terminology’, for people my age there is no connection between ‘idiot’ meaning stupid and ‘idiot’ meaning ‘low cognitive abilities’.
Perhaps younger generations will use mong and spaz as we do idiot and moron. Perhaps they will die out. It certainly makes me feel uncomfortable just thinking about my children using those words, but language does change as has been shown several times on this thread (and previously, as we’ve had this argument before).