Price discrimination is the means by which a producer captures the consumer benefit to trade.

Let's go back to Econ 101. Draw your price axis vertically, and your quantity axis horizontally. Make a big 'X' for supply and demand curves. Draw horizontal and vertical lines through the intersection point in the X to the axes.

You just found the market-clearing price and quantity.

There should be a triangle above that horizontal line and below the demand curve. That area represents the consumer benefit to trade. It's what people would have paid, but didn't have to. Below the line and above the supply curve is the producer benefit to trade. It's extra money people got above what they would have ordinarily accepted for their goods.

When a supplier has multiple price levels, it is trying to capture more of the total benefit of trade by grabbing rectangular chunks out of the consumers' area.

The fair thing to do is set one price for everybody, exactly at the market-clearing price. When you take the consumer benefit, they have less money in their pockets than they should, and that distorts the demand curve for every other good and service in the market. You are essentially waging war upon every other supplier, for the money of every consumer that does not participate in producing your specific good.

The cinema should price tickets such that they fill every seat in the viewing room by showtime. (Or actually, for information purposes, try for one empty seat.) If you price-discriminate, the people who paid the most for tickets might not be buying popcorn, or eating out at the restaurant across the street before the show, or grabbing ice cream afterward. The "fair" way to get more of their money is to try to sell them more goods and services than the cheapskates. Upsell them on first-class seating, or let them buy the right to request a 10-minute intermission so they can hit the bathrooms without missing any of the show, or give them organic popcorn with grass-fed butter instead of diacetyl-flavored soybean oil.

As both a consumer and a producer of other goods, I say it is bullshit, it is wrong, and it should stop. It is not quite as bad for me as it is for other people, because Amazon employs a lot of software professionals directly, but it is undeniably anti-competitive behavior. If every producer did it, people would buy less of everything, because as consumers, they would seldom see any benefit to trading. We would be wasting quite a lot of time haggling, and end up with fewer goods and services.

Your cinema argument comes from the perspective that the owner is somehow robbed by trading more. If the fixed price is 10, he earns 20. If it is 7, he earns 84. If it is 4, he earns 52. His supply curve is not flat. It is more stair-stepped, representing the fixed costs of opening an entire viewing room, the smaller variable costs of maintaining it for smaller or larger audiences, and stair steps for adding additional viewing rooms for a single show. He can calculate that supply curve based on costs and profit margins. Sussing out the demand curve on any given night takes some guesswork and price titration. Once you find the market-clearing price, you can drop all the discounts and coupons and market research and make that the one price for everyone, and occasionally wobble the price a bit to see if tastes have changed any.

That is not what Amazon is doing. They are segmenting the market, not trying to clear it.