See also Moron, imbecile, and cretin.
All Originally medical terms, that then entered comon usage as insults, fell out of favor medically because of that, were rejected by polite society, then after a refractory period and enough replacements, became lower grade insults that were more acceptable for common use.
How is it a slur?
It’s demeaning to an entire population. Pretty much the definition of a slur.
But “idiot” has the same origin and isn’t a slur?
See also Moron, imbecile, and cretin.
All Originally medical terms, that then entered comon usage as insults, fell out of favor medically because of that, were rejected by polite society, then after a refractory period and enough replacements, became lower grade insults that were more acceptable for common use.