Clarke

Moron: in psychology and psychiatry to denote mild intellectual disability. The term was closely tied with the American eugenics movement

Idiot: in legal and psychiatric contexts for some kinds of profound intellectual disability where the mental age is two years or less, and the person cannot guard themself against common physical dangers.

Imbecile: in psychiatrist contexts is used to denote a category of people with moderate to severe intellectual disability.

Are you really taking the high road here by using outdated terminology that’s more demeaning that the more modern replacement.

I think we can all realize that this man is stating that these people are slowing the progress of society and attempting to retard it’s progress not disparaging the less capable en mass. I really think you should look into the etymology of some of your other suggestions.