That's fine in theory but I don't see any basis for claiming that Amazon was selling anything below cost. Their costs on a per unit basis are tiny so they don't need much of a markup and ebook prices aren't that much less than physical books. The fact that publishers had more control over prices in the old model doesn't make Amazon a predatory monopolist.Selling products for losses ultimately harms consumers in the long run. Amazon only got a monopoly on e-books because it sold them for losses.
I have no problem with a company selling hardware for a loss like MS and Sony. But selling content for a loss harms content providers.