So you're saying that this company, which is playing by the rules (in that they aren't breaking any laws with their hiring practices), ought to make a move away from the practices that made them a hundred-billion dollar company because you feel that it's immoral. Do you see how that might look somewhat idealistic and, dare I say, foolish?
I never supported the 'Occupy' protests mainly because you can't influence a corporation by yelling at it. Sitting in front of those banks in NYC or wherever didn't actually change shit. You know why? Because businesses are not in the business of making people happy. Shocking, but true. Businesses are in the business of business, which is to say they make money. Some day I'll write down something that I hope will illustrate in simple terms how huge corporations operate, but today is not that day.
My point is that successful corporations, a group to which Amazon.com obviously belongs, are motivated first, foremost, and entirely by the almighty dollar. I'm not going to argue about whether or not that should be the case, but you are an idiot if you don't believe that that is the case. So if you want to alter the way that big corporations work, you need to either change the rules to make it more profitable to support what you feel are moral hiring practices, or you make it actually profitable to retain these sorts of temporary workers for the long term.
But shakin' your fists ain't gonna work.