Amazon is NOT a monopoly. A monopoly is when one company, or a small group of companies, control the supply of a product/service/etc. in a way that harms the consumer. Amazon does not control any supply and it is not harming the US consumers. First and foremost, in the grand scheme of things Amazon controls only a small segment of retail itself. In 2013 US retail spending was $5.4 Trillion. US E-Commerce sales totaled $263 Billion. So even if Amazon was the sole eCommerce site used by everyone in the US that would still amount to only 5.8% of all US retail.
The true monopolists in the book industry are the publishers. Let's examine the Amazon/Hachette spat in detail a little. Amazon wanted more freedom to price eBooks cheaper and Hachette objected. That's the core of the argument right there. Now let's take a look at some of Amazon's behavior during this spat:
1) They stopped taking pre-orders for Hachette books. Since Amazon no longer had a sales agreement with Hachette, it would seem logical that they would not want to take pre-orders and then be unable to fulfill them since its stock of these titles would be at Hachette's discretion and not at a mutually agreed upon level.
2) Amazon stopped stocking Hachette titles as much. So? Where is it written that a retail store must carry the products of a vendor with whom it has disagreements? Other retailers reported upswings in purchasing of Hachette titles during the negotiations with Amazon (it took 6 months). People were still able to get the titles.
3) They stopped discounting Hachette titles. Discounts has been Amazon's thing, it's why most of us shop there when we don't need the item right away. But let's really examine this one because it is the pièce de résistance. What Hachette was complaining about was that Amazon was selling Hachette's books at the price Hachette set for them. Keep that in mind, because Hachette wanted Amazon to sell eBooks at the price Hachette set. Translation: Hachette wanted Amazon to sell eBooks more expensive than they had to be (something Hachette, five other publishers, and Apple got nailed by the Department of Justice and several State Attorneys General for) in order to subsidize their print sales which is what Hachette is trying so hard to protect because the barriers of entry to the eBook market are substantially lower.