How will I ask for carrots when in Wales then?
Seriously though, some words evolve and lose ‘original’ meaning over a very long time. I’d never use retard, spastic or mongol as insults as I have known them used as a medical terms in my lifetime. Moron and idiot are not in the same bracket, they are terms for general stupidity (I appreciate they have also been used to describe low intelligence rather than just stupid in the past). Both have original roots in meaning ‘foolish’, and the current definition for both is ‘stupid person’ and is in no way used for medical diagnosis.
Younger generations would in no way associate moron with those of genuine low cognitive ability, and there is no value in making words taboo just because they had a different meaning before many people were even born.