IMO this is a terrible stance. If you buy a book that's got (legal) "offensive and harmful language or narrative" and you don't like it, that's your problem. If there's enough of a market for special bowdlerised versions for sensitive grown-ups then sure, go nuts, as long as they're properly labelled as such. But when it comes to the standard versions of books, at least those intended to be read by adults, I don't see why your personal sensibilities should override my preference for standard, unexpurgated versions of works — i.e. getting the product I believed I was paying for. "Ordinary people" reading for "pleasure" don't all necessarily want nice easy prolefeed, sanitised for their comfort.
Maybe any time publishers decide to change content, it could be noted in the website description, or maybe on an internal change log or something, so I know what I'm actually buying. They already have information about the edition — they could add short descriptions of revisions, like if it's been lightly edited for spelling and continuity, or edited to remove harmful stereotypes and offensive terminology, or edited to adjust monetary amounts for inflation and update illustrations, or whatever (that last one drove me nuts with the Famous Five — the copies I read as a kid were, I think, a mix of 50s, 70s and 80s, so they swung about between things costing 43p and 2/6, neither of which was relatable to 90s prices anyway, so you wonder why they bothered).
Or leave the text as it is, barring minor corrections, and stick a peel-to-reveal content warning on it if you like. I don't care, I just don't want to buy a book that originally contained something that I should find upsetting or offensive, except someone's made it all nice and clean for me so I don't have to confront the fact that upsetting and offensive things happened and still happen.
Younger kids' books, yeah, I can see that it's either update or delist, in a lot of cases. But we're big boys and girls now, with access to more information than any previous generation. We can make informed decisions about what media to consume.