I think it's generally pointless, spiteful, and only harms ordinary users who might someday have found value in coming across your old posts on Reddit from a search. It doesn't harm Reddit itself, the "value" of your individual account is very small compared to their vast archive. And they still have it, deletion just removes it from the public-facing front end. If the reason you're deleting it is because you don't want AI to be trained on it, that ship has long ago sailed. There are downloadable archives of Reddit floating around that it will never be deleted from.
So I wouldn't bother.
They're chasing profit too, though. "Taking a stand" means they're advertising, trying to differentiate themselves from their competitors and draw in people who hold anti-AI views.
That will last until that segment of users becomes too small to be worth trying to base their business on.