It's usage is still changing, obviously , but for me it's a more difficult transition because of the 'deci'
Wikipedia says it may be ahistorical though. https://en.m.wikipedia.org/wiki/Decimation_(punishment)
It also notes "In modern English, the word is used most commonly not to mean a destruction of a tenth but rather annihilation."
Sometimes prescriptivism is pretentious nonsense (like hypercorrection), status-seeking bullshit, or bullying masquerading as erudition, but sometimes it's just an explicit contribution to that ongoing negotiation and consensus.
When one of my students submits an essay containing the word 'over-exaggerate,' I correct it, striking out 'over-.' The word appears in dictionaries, so in that sense it's standard, and my correction is wrong, but it is an ugly, stupid word and should never appear in academic writing (and literate college students should know that). In my students' writing, it has increasingly replaced the simpler, better "exaggerate."
It's my responsibility as a teacher to encourage my students to think about the choices they make and the language they use, especially in an academic context, but I'm also hoping to cultivate the habit more broadly of just thinking about their choices, understanding that there are choices, and recognizing that the alternative is to be at the mercy of whatever consensus they're receiving from pop culture.
In most contexts, outside of a classroom, I won't bother with the correction, because it would be obviously unwelcome and inappropriate, but it has its place.
The line between descriptivism and prescriptivism is also very porous. Usage largely determines correctness, so unless you want to throw correctness completely out the window, there are going to be gray areas where either usage isn't widely agreed or where it really is necessary to correct language that falls afoul of standard usage regardless of whether the incorrect use will eventually be deemed correct.
Anyhow, 'disinterest''s disputed sense fills a hole in the language: 'uninterested' is a word; 'uninterest' isn't. People have solved the problem by collapsing the two words into one -- so that 'disinterest' and 'uninterest' are synonyms -- and throwing away the meaning of disinterest they use less often.
If I accept this, English loses some of its complexity and color. I don't want that.
Moreover, key texts and concepts become harder to appreciate if its sense corrupts this way. What do people think "disinterested justice" is if they don't know the meaning of the word? This kind of literacy is, I think, a basic building block of critical thinking. One can't think effectively, particularly in a social (political) setting, if one can't use words effectively.
I'm also not super convinced that people won't be able to understand concepts like "disinterested justice" because there's plenty of other terminology for that like "impartial" that are arguably much more common; I'm honestly not sure I've ever heard the term "disinterested justice" before now. I can at least see the value of that viewpoint being expressed even if I don't agree with it though, so in retrospect I should have responded before directly to the comment about "decimate" rather than replying to your response.
"Ironically, the earliest recorded sense of disinterested is for the disputed sense."
An example would be saying that someone was "disinterested" in what was happening on TV, or in music that was playing.