Imagine all the warehouse workers and local delivery drivers that will be required to make this work. It is good for the economy as it transforms.
Amazon is just the latest big boy. eBay was huge and is fading. Walmart is trying to keep pace with Amazon, but it is not easy.
The Chinese have Alibaba, already popular in other countries.
There will be competition....and competition is good.
My cheap Canon printer/scanner died a couple of months ago, and coincidentally (?) such printers disappeared from Walmart. Amazon had some at triple the price Walmart used to have, plus shipping. Last month those cheap printers suddenly appeared at the Walmart store at about the same price they were months ago ($35). Amazon now sells them for about $12 more with "free shipping" (not Amazon Prime). If you paid for shipping the Amazon cost would be about triple. In my experience, Amazon "free shipping" is painfuylly slow (2 weeks or more). Amazon socks are a better deal for me than Walmart though.