slurs are both harmful and not expressive: say what you actually mean instead
An lj friend of mine was pondering pejorative use of words like 'lame' and wondered if "by stripping (colloquial or written) language of everything that could possibly offend anyone ever, you're stripping it of tools for expression that can't necessarily be replaced." I don't want to strip language of tools for expression, of course, but I think one can easily tell if negative use of a word might cause suffering by asking the question "does this word depend on the assumed inferiority of a group of people to be meaningful?" If so, one could then make the argument that if it caused only a little suffering and provided benefit by being expressive, it might be worth it; however, I do not feel that commonly-used invectives are expressive. For instance, most people who use the word 'lame' to mean 'negative/inferior' aren't thinking "people with disabilities are unpleasant/inferior just like this situation, therefore this is an appropriate term" (which would be expressive as well as overtly prejudiced), they're just repeating a term they've heard used with no thought as to the connotations of the word. Being expressive involves thinking about the meaning of what you are saying and the impact it will have on who you are speaking to (among other things).
I also think derogatory use of person-descriptive words has the effect of reinforcing social stigma, and I consider the slimmest risk of reinforcing negative stigmas to outweigh any enjoyment/camaraderie that might be found in using a culturally-approved insult.
Furthermore, I consider short judgment statements to have no purpose. When people say "That's [negative adjective]" they're not actually saying what they mean. Often they mean "I don't like that" or "that makes me uncomfortable" or "I wish this was different" or "I feel for you, that situation would upset me too" -- but instead of expressing feelings directly, they pronounce a judgment as if it were a fact. One is supposed to intuit what they mean by this vague judgment. Saying "That's [negative adjective]" all by itself has no real meaning -- and if you go on to explain, it becomes unnecessary. Calling something 'retarded' or 'gay' or 'lame' is a sideways way of saying that one doesn't like it; it would be much clearer to state exactly what one doesn't like and why and how it makes one feel. It's also more vulnerable though, so I can understand the impulse to make a judgment statement instead of an emotion statement. Since I came to think this way there have certainly been times when I've been silent where I would previously have made a judgment statement, because I couldn't bring myself to express my emotion on it (either because I was feeling vulnerable or because I worried that expressing my feelings would seem intrusively personal to the person). I feel that silence is a better choice for me than judgment, and I feel also that it motivates me to practice openness. (I sometimes resort to saying variations on "that's horrible" but my goal is to express feeling instead)
And as far as the emotional side of this, it upsets me to hear someone describe something as 'retarded' or 'gay' or 'lame' as a way of expressing negative emotion, because I feel that that is a careless insult to anyone who might be accurately described by the literal definition of those words. I know that, for example, not all gay people would be offended by someone saying, "that's gay" in a disparaging way, but for me that's irrelevant. Even if it is unintentional AND misses the target, it remains an insult. I believe intensely in the power of words and when a word is uttered in a negative context over and over, I believe it sends negative energy to everything attached to that word. So it makes me cringe because I feel like every time someone does that, it hurts people, even if no one is consciously aware of it.
ETA: not to mention, there are people for whom these words are triggering because they often are used in abusive situations. It is not okay to express yourself sloppily and risk causing someone to have a PTSD flashback when you could just be a little more creative and honest instead.
This sort of builds on my thoughts on 'curse words' (which I wrote over 5 years ago so don't judge me on the rather scattered and unsupported quality! it needs re-writing, but it pretty much gets the point across).
Replacements for the ableist slurs "retarded" "herpderp" "crazy/mental/insane" "lame" "dumb/stupid/idiot" (includes links to why those are ableist)