One of my pet peeves are people who knowingly re/misdefine words and concepts, in order to manipulate others.
Indeed. The word "gay" appears in popular Christmas carols and had an entirely different meaning from today's common usage. So too "progressive", "liberal", and a host of others. For example, it's now necessary to use the modifier "classic" to identify that you're speaking of what was commonly known as liberalism just ~100 years ago. It's extremely annoying when perfectly good and long-established words are hijacked for someone's agenda.
Disclaimer to assuage the cancel culturists: This is not a comment on anyone's politics, just a eulogy for the loss of - dare I say it - diversity in word choice.
In Oz, we have a political party called the Liberal Party.
They have, historically, been true conservatives, much closer in philosophy to the British Conservative Party, than to others parties with similar names.
They have drifted somewhat further right in recent years, making the name even less valid.
As "conservative" is just a label, traditional conservatives don't have anything to distinguish them from others that are quite a bit more radical, so the term "conservative" in this country has come to refer to the "right wing" of the Liberal Party as well as others even/much further from the mainstream.
Thus, we have the situation where the media has to call more left wing people "small 'L' liberals."
Much of this is because various people have seen fit to shoehorn current US terminology into Australian politics, where the meanings don't neatly fit.
Of course, "cut n' pasting" of US material is a cheap way for smaller groups of whatever persuasion to appear to have a presence on line.
The dumb thing is they don't do "due diligence" when it comes to editing the result, so their followers end up perpetuating the misuse of terminology, further distorting the meanings of words.
Your example of "gay", though a common one, is not as new as you may believe.
I read an American novel written in the late 1950s, where it was used in that sense.
Even disregarding that one as an "outlier" , it has certainly been in common use in Oz since, at least, the 1980s.
When a ice cream confection was launched called "Golden Gaytime", it caused many a chuckle.
Interestingly, they still make & sell it!
A common term back in the1960s, synonomous with the modern use of "gay", was "camp".
That term has morphed into one simply meaning "showy, extravagant, "kitschy".