I've worked in a couple warehouses and have a lot of friends and colleagues who have, too (I never worked for Amazon, but a lot of said friends and colleagues did). The consensus is that Amazon's treatment of its warehouse workers is about as bad as it gets. There are plenty of warehouses that take employee safety seriously, that pay well with decent benefits, that allow their employees to take restroom breaks instead of forcing them to resort to pissing in bottles at their pack stations (seriously, Amazon, what the hell?), that put at least some semblance into temperature control (as difficult as it may be to do in a large building like a warehouse) and that overall treat their employees like human beings instead of machines.
It's good to be skeptical of the treatment of workers as a rule, but there are definitely different circles of Fulfillment Hell, and working for Amazon's pretty damn close to the inner-most of those circles. Amazon does pay better than average, but there are apparently few companies that treat their workers worse (at least in the US).
I did a lot of research about the 'picker industry' for that case. What a nightmare job. I can't imagine having to work somewhere like that with all the rules, quotas, bully leadership, favoritism, etc., worse than the Army.