And that system of changing names doesn'thelp at all.

Look at the spanish evolution for mentally handicapped:

tarados - ... - retrasados - ... - discapacitados mentales

I can't recall them all, but them all were words that meant something not specially offensive, in this case:

imperfect, defective - ... - retarded -... - mentally handicapped

None of these were insulting in its time, they were PC, but with time these words have became kind of insults because the meaning that is behind slowly infiltrates the words making them kind of obscene.

Maybe "Mentally handicapped" will be an insult in some years and somebody will say it's cruel to call them that way and suggest "light headed" or whatever prudish or prissy new name they invent and we'll all have to call them that way or be considered non-PC.