> eBay deciding unilaterally that people can't buy or sell already-printed copies
eBay is not "unilaterally" deciding anything. I can't remember the last time I bought or sold anything on eBay for instance. As I see it, they probably want to avoid the resulting controversy from any of these items, and don't want anything to do with them on their platform.
As an immigrant to the US, this is what I don't get. Isn't the whole idea of capitalism supposed to be that eBay's delisting is an opportunity for ten other websites specializing in obscure Dr. Seuss books to pop up and eat their business? [1]
Or would you rather have one centralized government agency in charge of deciding which books can and can't be sold?
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[1] What I personally suspect (without much evidence) is that there is very little of a secondary market for these books. Sure, some are going for $500 because people will collect anything, but the person simply doesn't care about them one way or the other.