Earlier quoted context omitted.
Retarded is not a slur. Never was. People keep picking arbitrary words and saying they're "offensive", but there's no reason why. I have heard kids call each other "mentally challenged" and "developmentally delayed", I kid you not. Younger kids have trouble pronouncing those, so maybe that's something? Anyway, I refuse to partake in the euphemism treadmill.
My Midwestern upbringing was certainly peppered with people using ‘retard’ as a slur, so... mileage may vary?
What's being said here is that the word retard is an insult, but does not rise to the level/strength of a slur.