I see the points, and I myself never use the word, but exactly where does it stop? Where does one draw the line between acceptable and unacceptable?
lougle says retard as a noun is never acceptable - but what about things such as flame retardent or the musical use (a retard in music is a point where the tempo slows) etc?
Someone earlier said that "tardy", as in late or (physically) slow, was alright, but it comes from the exact same route (eg modern French: en/du retard - to be late), in much the same vein as words such as moron / imbecile.
I've seen many posters on here, when talking about words such as "cretin" say that it doesn't matter what it's modern use is, the historical use is awful and ergo any use in any context is unacceptable. But in this thread, posters have said that some use is alright, others isn't, as it depends on context.
Do you see where this causes confusion and problems in thrashing out exactly which words are acceptable and which aren't? I genuinely believe that most people really aren't intending to be horrible if they use one of these - if, of course, someone yells a word as an insult in the street, completely wrong. But I wouldn't be expected to be taken to task for (for example), using the word faggot in the butchers.
National borders can also change popular use and meaning, and in our increasingly global society, it can be hard to get it right 100% of the time.
Like I said, I don't believe most people set out with the intention to hurt. Some do, but they're arseholes, and they will be no matter what phrasing they use. I also don't think people should be crucified for questioning what may be long-held understandings. Humans are fallable and language is large and complex.