If you're legally allowed to pay people $4.95 a week and work 'em at gunpoint, that becomes the new maximum efficiency point (provided enough humans and/or robots can be procured) and the existing Amazon goes out of business, unable to compete.
For that matter, if Amazon permitted just anybody to grow and work their way up, there'd be a lot of warehouse people or code-mongers thinking they should prosper, and there's not room for all of them. That's basic economics too, and it means that no, you can't work your way up nor can you grow. There's already a Jeff Bezos, and you're not it. There's also a 'your boss' and you're not that, either.
So, the practical implementation of human worker wages remains very interesting to people, and the fact that Amazon's the best at arbitraging this dynamic is relevant.
What you see as outrage is simply people's reactions to that very basic economics: to what extent can a company define the conditions for an industry (or all of society) by exploiting the rules and running as close to the edge as possible?
One assumes there's a spectrum and that you can get a 'good job' and have less misery than your fellow worker, if you try hard or you're lucky or wealthy or nepotistic enough. One also assumes that if you 'work your way up' you're wealthier and have it easier and can live large like some important person.
Amazon flips that on its head. If you're in the Amazon model, there is no 'up'. At every level, you're existing in maximum tolerable misery because that is your global strategy to outcompete every other business entity that threatens you or could ever threaten you. If you're 'winning' as an individual, that hurts the company: the company wins if everybody from bottom to top is struggling in the optimal misery/output balance, to the extent of applicable laws.
It's a conversation worth having. This is the formula for corporate efficiency, but to what extent should humans operate NOT at the point of maximum misery?
The American Dream is an intangible. If other people aren't impressed by it, then offering it as primary compensation is disingenuous. I'm particularly dismayed by trying to mandate it… it's a pretty lame dream if you look at things in a more systemic fashion. It has already led to the collapse of the American middle and lower classes, and this is only accelerating.
An American 'oh, hi, I'm awake now' might be a wiser alternative…