Far be it from me to imply the language doesn't change and slang can't change the meaning of a word for good. My mother and I used to argue "that sucks" with me taking that very tack. ("But Lauren, do you know what that means?") I argued that if blowjobs were actually the etymology of "sucks," which I wasn't convinced of at the time, the word had long ago branched out from that meaning and the usage synonymous with "that stinks" should have no horrifying connotations to anyone. If oral sex wasn't in the mind of those who used the expression or those who heard it thus used (my mother excluded, apparently), then in some quite meaningful sense (yay for postmodernism), it didn't mean that anymore.
So I can certainly see the appeal of an argument from postmodernism, that the word "gay" has a new meaning ((3) stupid) in addition to (1) happy and frolicsome and (2) homosexual. However, I think it's clear that, whatever connotations definition three theoretically doesn't have now, it definitely arrived in the lexicon through pejorative application of gay definition number two. (This is where the previous post becomes relevant!) It's apparent we lack imagination or a sufficient vocabulary in English (and probably every other language, but I'll stick to what I know) and so constantly lift from descriptors of other groups of people we don't like or (ding, ding, ding!) don't respect to describe anyone or anything negatively. ("Don't be retarded," "how lame," "I was gypped," "what a spaz," "she totally freaked.") So while the 14-year-olds saying "that's gay" probably truly aren't at that moment actually intending to offend or even comment on anyone who is gay and legitimately aren't considering that use of the word in this context, people who are gay or who have friends who are gay (or who are just old and so aren't desensitized to this usage yet) often can't help but sense the traces of its etymology. (It's significant to me that I have never actually heard anyone who is gay say "that's so gay" in any sense other than the obviously directly derivative sense that that's something so ridiculously sparkly and fabulous that only super-stereotypically feminine gay men would like it, so obviously not everyone thinks it's a word entirely without connotation in this sense.)
(I know it's super-cheesy, but I love this PSA.)
So now we come to the crux of the matter: do people have a responsibility to avoid saying things that offend others if they don't think they're anything that should offend anyone? On the one hand, you never know what might offend someone; virtually anything you could possibly say would offend someone for some (probably initially bewildering) reason. (Stupid example: if, as I age, anyone younger than me ever refers to me as "this young lady" in that slightly-ironic-to-be-nice way (because heaven knows being old is an unspeakable horror best ignored by exaggeration in the opposite direction), I'm going to clock them.) I do, however, think political correctness can go too far, and it's probably not a worthwhile use of one's time to bend over backward trying to keep from the slightest possibility of offending anyone. However, I do think it's very important to think about how the words you use came to have the meanings you impute to them, and especially if someone tells you they find something offensive, you should seek to eliminate it (at the very least in their presence).
One friend of mine in particular often argues the other side of this point to me. He'll say something sexist that I get offended by and then spends half an hour explaining why either he's not being sexist or why I'm too easily offended. Similarly with "that's gay"—he thinks people are being overly sensitive and it's not his job to be sure not to offend someone who's 'looking' to be offended. It seems to me he and others are taking the Eleanor Roosevelt approach ("No one can make you feel inferior without your consent"), which I've always found to be terribly annoying and entirely untrue (or, if possibly true, to place an undue burden on the person feeling inferior). To a significant extent, it doesn't really matter if you understand why someone is offended; if they are, they are, and if you like them, stop!—even if you think they're being overly sensitive.
I think the reason people try to justify things they're told are offensive is simply because nobody thinks they're sexist or racist (or ageist or ableist or prejudiced in any other way), so when it's brought to their attention that someone does find something they said offensive in some way, they are so horrified or uncomfortable that someone thinks they're that sort of person that they feel the need to explain how they're not really. Cut your losses; you cannot win this one. Nobody's going to think you're incorrigible if they say, "That's offensive" and you say, "Really, how? Oh, wow, I didn't think of that"—the end. Being increasingly offensive as you explain how you're not actually being offensive or how it's their own fault they're offended, however, won't win you any friends.
There was a Motherlode post/discussion a while back (because, yes, I'm ridiculous and read a parenting blog despite having no intention of procreating for some time, if ever) that I found quite germane to this discussion. It's about classroom assignments (in particular, that one where you make charts with traits from your parents and yourself to learn about heritability—you know, if you can curl your tongue; whether your earlobes are free-hanging or connected to your head, etc.) that are potentially awkward or discriminatory (in this case, to adopted kids...or those conceived through donor sperm or eggs or anyone who otherwise doesn't have access to both biological parents). I thought the post to be quite interesting, as I'd never really thought about that problem, and it seems plain to me that if there are things we as a society are doing that make people feel bad about themselves (or unable to participate!), if there's any reasonable way to avoid that, we should. (It should be noted the post offered other options with the same educational value that could be easily substituted.) Many of the commenters seemed less charitable:
"[A]doptive families are by far the exception, not the rule. So you're demanding to change the system entirely, just to satisfy a small minority?"
"My gosh, if I got frustrated and angry over one of my Kid's homework assignments because it didn't pander to my special situation, I wouldn't make it as a parent."
"Goodness gracious the things we manage to find problems with in our society. Count yourself lucky the issue you have to write about is a genetic work sheet your elementary aged child fills out. So much complaining so few real problems."
I think all too often people like these commenters miss the point. It's not the case that (most) people just sit around looking for things that an argument could be made discriminate against some specific situation they are in or quality they have in order to cause a stink and get special attention and pity. In most cases people are truly saddened/disturbed/hurt by whatever everyone else is assuming is universal and bring it up because they assume nobody's trying to hurt anyone's feelings, that the apparent blitheness with which they're being disregarded is simply because everyone else, not being in that particular situation, is simply unaware that they're hurting anyone. (Which discussion unfortunately too often triggers the "But I'm a nice person!" defensiveness and rationalization...) Nobody's asking that the sensibilities of the smallest minorities be allowed to dictate the majority's actions but just that people show some awareness of the fact that not everybody is like them. Presumably since we're not all ogres, they would then have some willingness to adjust if the adjustment wasn't onerous. Obviously nobody is aware of every possible potential offense they could give anyone else, but that's exactly why people do and should inform others of things that make them feel slighted.
Back to language, though: my question is whether all words that were ever offensively intended should be off limits forever after or if there's a sort of statute of limitations of offensiveness. "That's gay" and "what a retard" are definitely still too loaded to touch for those of us who don't want to offend, but what about "moron"? My inclination is that since that word hasn't been used to refer to an actual medical condition in my decades, it's officially decoupled and is thus acceptable (same with "lunatic," "idiot," etc.—of course, I may lean toward their acceptability simply because they're words I regularly use and I'm being defensive). I remember my mom getting mad about my use of "spaz" (see: spasticity), which was the first time I was made aware of an offensive aspect of a term I regularly used. Then (only a few years ago) my brother called me out on "gypped," which is obviously (in retrospect!) a reference to gypsies. Nobody has actually said anything to me about "lame," but it is certainly also offensive. I guess my problem is that I started using all these words solely in their slang senses and at a relatively young age and either never thought of their original meanings until years later or was simply unaware of the etymology at all (I'm pretty sure that conversation with my mom was the first time I ever heard the word "spasticity"; I had no idea it was a real thing). So I feel that since my speech developed using them in an innocent sense, it's somehow acceptable for me to keep using them. But this is exactly the point! I'm sure that's how teenage guys feel about "that's gay": if they don't mean to be saying anything about homosexuality and are possibly actually entirely oblivious of the connection, we should just ignore the offensive overtones.
It's immensely annoying how few legitimate words the English language has for certain concepts. ("Good" and "bad" are especially bereft. "Fantastic" doesn't mean "good," it means unbelievable, a fantasy. "Great"? It means big. "Awesome"? Inspiring of awe (/terror)—in fact, basically the same as "awful." Similarly, "terrible"? Inducing terror. "Horrible"? A horror. None of these words actually mean "good" or "bad" in varying degrees; they mean different concepts entirely.) It seems the ideas of "stupid" (whether expressed as "lame," "gay"—or, you know, "stupid") and of an unpleasant or unthinking person are actually impossible to express directly, without loaded reference to groups like those already described. People often disparage cursing, saying it shows a lack of creativity in vocabulary, but is it actually possible to use an extensive vocabulary to replace all vulgarisms? I'm starting to think not, and that's utterly depressing.