People like the idea of a truly free market because it creates competition and reduces homogeneity which generally creates more adaptability and freedom of choice in various situations for consumers. With Amazon owning everything they will no longer have competition because they will continue raking in money until they have enough buying power to crush anyone who opposes them and there will no longer be any diversity of companies performing the same services in the marketplace so if you don't like Amazon's way then you just have to go pound sand. Also, as they get more money, they'll start lobbying the government to create more corruption as they dodge taxes in other countries etc. There's lots more problems but if you play the board game Monopoly towards the end when one or two people are taking all the money, that's basically what it creates in real life.