They're not banning the books, they simply won't allow them to be sold in their store any more. Almost every store in the world makes decisions on which products they wish to sell, and which they don't, so you'll need to also share your outrage with pretty much every online and brick-and-mortar store out there.
Also, 1st amendment prohibits the government from infringing on your right to free speech, within certain limits (see the classic "yell fire in a crowded theater example). It does not give you the right to sell what you want on a private store platform. You'd be hard-pressed to make a case that selling something for money is a form of self-expression, and eBay is in no way a government institution.
I don't really agree with the removal of these books, I would rather see them continue to be published, but maybe with a preface or footnote. Erasing evidence of racism doesn't erase either the fact that it existed, or that it continue to exist. Far better to acknowledge the past, and repudiate it. That said, eBay's platform, eBay's rules.
