Ok, antitrust laws are not there to protect quality, they are there to protect price.
Not at all true. "The United States antitrust law is a body of laws that prohibits anti-competitive behavior (monopoly) and unfair business practices. Antitrust laws are intended to encourage competition in the marketplace." (from Wikipedia).
If a company with a dominant market position drops prices in order to force competitors out of business, that would be anti-competitive behavior, and thus subject to anti-trust action in spite of the fact that it lowers prices (in the short term).
In this specific case, it can be argued that Amazon has achieved a dominant market position in book-selling, and attempts by Amazon to set market pricing could be anti-competitive. Thus counter-efforts to break Amazon's ability to force market prices could potentially be favorable toward overall competitiveness in the marketplace.
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Amazon is running the brick and mortar bookstores out of existence by pricing the products they sell, below their cost. Predatory pricing, with the intent to destroy your competition is a crime. Amazon is driving the cost of books so low, it is running the publishing companies out of business, greatly reducing the quality of editing in books. (Editing is as important to the quality of a book as writing. It is more so for new authors.)
If Amazon is not stopped, they will soon be the only book store and the only publishing house. That is not healthy competition.
This is absolutely the concern. If a company achieves monopoly power by driving out the competition, prices then go up, inevitably. There is no reason for the monopoly to keep prices low win the absence of competition. Micro-economic pricing theory firmly proves that monopolies increase profits by increasing prices, for any realistic demand curve, in spite of the fact that unit sales drop due to the price increases.