If Amazon stopped engaging in price fixing, then people like you who aren't shopping on price could still buy stuff on Amazon, and other people who are shopping on price could buy the same item from the manufacturer's site for 30% less with the knowledge that it'll probably arrive in a week rather than in a couple days. I'm not sure what problem you have with that.
It's not price fixing. The seller is still completely in control of the price, but they cannot discriminate against Amazon by selling it cheaper elsewhere. Or they can, but then Amazon don't want to do any business with them.
These kind of contracts are standard for all kinds of third party marketplaces. You don't have to sell through them if you don't agree with the contract.