These days any given new graduate who didn't attend an ivy league is in a situation where it is extremely difficult to get a job.
The alternative to working as a contractor at Amazon is not working at all. This is the situation these contractors are in. When the alternative is being in extreme debt / homeless, a choice cannot be made freely. This is the situation that Amazon and Walmart are taking advantage of, employee these people as hourly, no benefits contractors.
Obviously there's the argument that Amazon and Walmart are being 'good' providing them with hourly pay when they would otherwise be paid nothing. This, however, doesn't mean they're not taking advantage of the people they hire as contractors. I would also not argue, but hold as a belief that it is extremely immoral to not pay the people who are struggling to help the company succeed, in order to pay people who are already wealthy more.
Before you explode with economic principles of how they are being paid what they're worth due to the harsh job market conditions, save your breath, I already know. The thinking is right from a market philosophy perspective, but these principles also weaken the company, and I would say are actually wrong from a perspective of building and growing a successful business.