Bear in mind that being really crazygonuts evil is a weakness: it's a vulnerability, begging for legislation or boycott. There's absolutely not a direct correlation between evil and profitability, unless maybe you're a banker.
Amazon's a storefront. They have to serve two masters, one of which is the customer. The other is their reputation among capitalists and rivals.
On the one hand they must promise to deliver better prices and choices than other storefronts, all while assuring customers that they have happy workers and aren't doing anything horrifying.
On the other, they must continue to convince Wall Street and possible rivals that they're the most brutal tyrants on the block and will inevitably kill and devour ALL competitors, all the more because they don't pay dividends and earn people money based on their expansion alone.
Amazon's designed to use psychology to get all employees working like Spartans. If you see this behavior in a sports team, or in open source, typically you go 'hey, cool' and approve of the fierce eagerness to strive. It's part of the human experience and can be used in many ways.
If it's used to condition warehouse workers to accept a situation where they're compensated, but driven to efficiencies that kill a percentage of them, that raises the question of what's the responsibility of those managers. To run a group of humans at those levels of output requires coddling them to some extent, and 'giving them the choice' to walk away (but if you're compensating them even a little better than usual they'll get used to it and resist walking away, even at their own peril: especially if they're thinking Spartan)
This desire to perform and be part of a team isn't something imposed on humans by evil corporations. It's a natural human tendency, which is why Amazon's strategies work. What Amazon does is exploit that as hard as they're allowed to do.
Offering the chance to shill for part of your shift, and offering this only to an elite who're able to do it effectively, is a really clever social exploit. Will it continue to be allowed? Maybe. It's very much the kind of thing that's bending 'the rules' for their benefit, and to do it properly you kind of have to be Amazon. Remember that the whole purpose of the exercise is to further crush any competitors, including those who might have marginally better labor practices… or buy and destroy anything that might have better labor practices, for instance Whole Foods.
It's fair to argue that turning employment into a monoculture in which everything out there works this way (thus foul and no fouler, we hope) is a bad thing to do.