We agree to meaning to communicate and progress without endless debate and confusion.
SI is pretty clear for a reason.
We decidedly do not do that. There's a whole term for new terms that arbitrarily get injected or redefined by new people: "slang". I don't understand a lot of the terms teenagers say now, because there's lots of slang that I don't know because I don't use TikTok and I'm thirty-something without kids so I don't hang out with teenagers.
I'm sure it was the same when I was a teenager, and I suspect this has been going on since antiquity.
New terms are made up all the time, but there's plenty of times existing words get redefined. An easy one, I say "cool" all the time, but generally I'm not talking about temperature when I say it. If I said "cool" to refer to something that I like in 1920's America, they would say that's not the correct use of the word.
SI units are useful, but ultimately colloquialisms exist and will always exist. If I say kilobyte and mean 1024 bytes, and if the person on the other end knows that I mean 1024 bytes, that's fine and I don't think it's "nihilistic".
https://en.wikipedia.org/wiki/Language_planning
(Then you could decide what you think about language planning.)
I'm pretty sure any linguist will agree with this definition. All language normalisation is an afterthought.