There's probably a useful discussion about whether orphaned works should be protected by copyright.
But it's madness to suggest that once a publisher has published a book they're somehow compelled to continue publishing that book in perpetuity.
I don't think(?) eBay globally banned selling of past copies of Meinkampf while the copyright was cleverly held by a German State. Doing so is pretending copyright is a right that extends to sold property that is a copy, extending a right too far, while banning a class of books like MeinKampf for your own reasons is perfectly valid.
If they want to ban racist children's media on their platform then they should. That includes a lot of TinTin, popeye, Tom and Jerry, etc, that has never been classified as racist by some copyright holder.
edit- s/published/printed
Of course, if you believe that copyright should prevent the resale of goods, that's an entirely different story that ignores the current state of affairs in the world and the legislated rights of people in many countries (where there are such laws that prohibit limiting the resale of goods).
Well, after WWII, the USA engaged in their "denazification" of Germany, where they censored and burned Nazi materials.
Which side would you say they were on?
If as a society we allow companies, that are equal to (if not more powerful than) the government we elect, to pick and choose what parts of public discourse are acceptable or not, we have no one but ourselves to blame when this inevitably goes pear-shaped.
Like many other things in the past, what is legal right now may not be ethically and morally correct in the future.
You are correct that society as we know it does not cease to function immediately after the giants like amazon, facebook, twitter, ebay, etc. take a specific action like banning a book or banning a user. However, the longer term implications are far more concerning and the time to start contemplating these issues was yesterday (or any other time in the last few years). The next best time is now.