You are allowed to crush your competitors with economy of scale provided that you don't do it by selling at a loss. That's actually the entire point of economy of scale. The reference in the article is to passing a law against this so clearly what Amazon did is legal now. Furthermore, we don't need a law for this as this type of thing is well handled by a non-compete clause, which I am surprised wasn't in the seller's agreements with Amazon.
The larger issue is that Amazon does not treat each product equally. When you search for an item, they don’t necessarily even show you the “best item” — most bought or highest reviews. Products which buy advertisements or Amazon’s own brands are bubbled up: its not an even playing field in this sense.
