This set me thinking. I agree with it of course, but it occurs to me that the phenomenon of semantic drift is involved here. Words don't keep their meanings as time goes by, so for all we know we may in all innocence be using extremely offensive language to each other without any of us becoming aware. This is one reason why Middle English, which is English as spoken between the Battles of Hastings and Bosworth, is in my opinion harder to learn than the earlier Anglo-Saxon stage of the language, as spoken between Vortigern's invitation and the aforesaid Battle of Hastings. Here's a bit of Anglo-Saxon, from the prelude to Beowulf:
Hwæt! wē Gār-Dena in gēar-dagum
þēod-cyninga þrym gefrūnon,
hū ðā æþelingas ell en fremedon.
Oft Scyld Scēfing sceaþena þrēatum,
monegum mǣgþum meodo-setla oftēah.
Egsode eorl, syððan ǣrest wearð
fēa-sceaft funden; hē þæs frōfre gebād,
wēox under wolcnum, weorð-myndum þāh,
oð þæt him ǣghwylc þāra ymb-sittendra
ofer hron-rāde hȳran scolde,
gomban gyldan; þæt wæs gōd cyning.
Now this is pretty clearly like a foreign language to most of today's English speakers. If you were to go about learning what this meant, you'd probably do something like go to a class or learn it from a text book because you'd realise that most of the words are strange to you.
Contrast this with the much more recent (1380) late Middle English bit from the prologue to the Canterbury Tales:
WHAN that Aprille with his shoures soote
The droghte of Marche hath perced to the roote,
And bathed every veyne in swich licour,
Of which vertu engendred is the flour;
Whan Zephirus eek with his swete breeth
Inspired hath in every holt and heeth
The tendre croppes, and the yonge sonne
Hath in the Ram his halfe cours y-ronne,
And smale fowles maken melodye,
That slepen al the night with open ye,
(So priketh hem nature in hir corages:
Than longen folk to goon on pilgrimages,
And palmers for to seken straunge strondes,
To ferne halwes, couthe in sondry londes;
And specially, from every shires ende
Of Engelond, to Caunterbury they wende,
The holy blisful martir for to seke,
That hem hath holpen, whan that they were seke
The problem is not quite as severe as it might be because this is not as old as, say, the Ayenbite of Inwit or the Ormulum, and it's also in a dialect which is similar to the direct ancestor of modern English, but for instance the word "fowles" to us brings poultry to mind rather than larks and sparrows, "strondes" is clearly "strands" but to us the word "strand" used in a sense close to how it is employed here refers to the bank of a river and not a seashore, and so forth. Therefore we look at Middle English without recognising that it is still substantially a foreign language where they do things differently, and we are more likely to misunderstand it unwittingly rather than realise we don't understand it, which may be worse.
This is of course because of semantic drift. Words change their meaning over the centuries, and sometimes a lot faster. They may change them at such a velocity that people get irritated because it occurs noticeably within their lifetime. The classic example of this at the moment is of course "gay". To me, "gay" means "male homosexual" and I rarely use it with any other meaning, except in the fixed phrase "skip gaily", something I do rather a lot, where it does in fact refer to something I do which is perceived as a form of gender non-conformity or perhaps Morris dancing, but probably not. It's now so common to bemoan the change in the meaning of the word "gay" from something like "happy" or "glad" to "male homosexual" as to become a cliche. What is a little less obvious is that it has continued to shift in meaning from the usage I make of it. First of all, it broadened its scope to refer to female homosexuality, a usage which definitely seems unnatural to me and which I would never have used, and now it's drifting further towards a similar meaning to "lame". The word "lame" itself is of course disablist, but if an older meaning of the word referring to a physical disability had been lost, it wouldn't be any more, and language is of course dynamic. This leads me to suspect that there is offence in all sorts of places. Just as an inline footnote, I don't in fact use the word "gay" at all now because my view of the concepts surrounding it has shifted and I would now probably want to say "gynephilic" and "androphilic" and probably be met with incomprehension.
There are in fact words which have lost a meaning which would be seen as offensive nowadays by many English speakers. One of them is "nice". This is from the Latin nescio - "I don't know", and refers to ignorance and stupidity. By the Middle Ages, it was "nice", used in French to mean "clumsy", i.e. someone who doesn't know what they're doing, and then changed to "silly", i.e. foolish. I'm going to come back to the word "silly" because it's interesting. Later still, in the English language, which has borrowed a lot of French words, it came to mean "timid", then "careful" or "delicate". Around Shakespeare's time it gets difficult to work out what it means for a twenty-first century audience, then it emerges from the confusion to mean "delightful" and then in the twentieth century came to be considered too genteel and insipid to be easily pronounced without ridicule, partly due to class implications and partly because it was used more by women than men and therefore taken less seriously. In fact, along the lines of "women and men are the same and they're all men", it seems to have largely disappeared except possibly in erotic contexts.
To return to "silly", this is a word which to me mainly brings to mind the affection of a particular German of my acquaintance who discovered the word when on holiday in England and found it very amusing, which makes a lot of sense - unlike the other two it seems to be an intrinsically funny word. In fact unlike the other two, it has a cognate in German - selig, meaning "blessed". In fact it also used to mean that in English. The contortions of the word "silly" go like this. The prehistoric ancestor of English, proto-Germanic, used the word sæligas to mean "happy", from the root sæl meaning "happiness". By Anglo-Saxon times this had become gesælig, which is why I started with the ancestor of English rather than Old English - the initial syllable later disappeared. At that point it meant "lucky" or "happy", and of course the word "lucky" itself also meant "happy" and "happy" meant "lucky" (think of "happenstance") so that's a bit of a meaning cluster too. By the thirteenth century, it meant "blessed", then "pious", "innocent" and later "weak" or "feeble", and eventually "feeble-minded". However, it's now considered less offensive than "stupid", probably partly because it's considered to be a voluntary and temporary thing and doesn't refer to learning disability any more.
All of these words have drifted, sometimes so fast it's possible to realise they're doing so in a single lifetime. What seems remarkable to me about them is that they all seem to have passed through similar meanings. "Nice" originally meant "ignorant", "gay" meant "happy" and "silly" meant "happy" and something similar to "ignorant" at different times in its history. Another, weaker, example, is "blessed", which is sometimes used as a mild pejorative word similar to "silly", as in "that blessed thing".
It seems, then, that there's something about that group of ideas - happiness, foolishness and the like - which leads them to bleed into each other in the English-thinking mind, and I find that really intriguing. I also want to know if that happens in other languages and if anyone has any ideas about why that tends to happen.