The "R" Word

I like the word "retarded". This, of course, is a problem. I don't use it often, but there are situations where I feel called to invoke the voice of a jaded teen circa 1973, and nothing else gets the job done quite as well.

I know I'm not supposed to. There's a societal consensus on this, and, of course, writers and artists must always heed consensus preferences. That's our role: keep our heads down, tow the line, and stay within the bounds of politesse. Don't be bad. That's how artists roll. I get that.

But I'm not clear on the reasoning. I suppose the word is offensive to genuinely retarded people, but that usage doesn't even exist - the afflicted having been renamed - so I'm at a loss as to whom it offends, exactly. Perhaps simply non-smart people? We don't want to stigmatize low intelligence. But then why can I still say "stupid", or "moron", or "dope", or "lunatic"? Why can I freely shower my writing with "shmuck", "putz", "idiot", and "imbecile"?

I'd imagine the answer would be "Well, you shouldn't! These are highly negative, insulting and hurtful words, so they all should be avoided!"

Again, it's not that I'm not eager to diligently update my adherence to trendy social norms of expression. I just want to sensitively parse the ever-shrinking boundaries. So I have two questions:

1. Why is intelligence special? Shouldn't we proscribe "ugly", "clumsy", "untalented", "smelly", "limp-dicked", "flat-chested", and the many other terms stigmatizing deficiency and otherness?

2. Where do we draw the line? Frankly, "retarded" doesn't strike me as all that extreme ("moron" and "dope" contain far more venom). It's mostly just snide. So shall we expunge all snide speech, for example the description of a singer as "horrendously out-of-tune"? That's undeniably hurtful, no? Should she be "otherwise-tuned"?