Disclaimer: I'm not a legal expert, just an engineer with my own opinions.
I struggle with it as well because conceptually in my mind this is the same as a grocery store using customer buying data to inform itself. Grocery chains have been using private label brands to compete with name brands for years. Check your cereal aisle for the "fruit loops" in the back without a box that are ~50% cheaper than the name brand boxed real fruit loops.
I never saw this as wrong growing up. I saw this as the store offering a cheaper comparable and consumers were able to chose which they want. In fact, the grocery store also controls what is on the end cap and what is on top and bottom of each shelf.
I think the landscape is heavily skewed in favor of the dominant online retail merchant. This skew and dominance is what causes people to claim afoul behavior is going on.
Difference in quantity has a quality all of its own.
There are kinds of behavours that are acceptable for an individual or a single groceries store, but if a large company adopts it across the country and puts it in the policy, then they are beaking the law.
Grocery stores select which products they want to sell and have limited capacity.
Amazon provides a platform through which "everyone" can sell "anything" with no tightly constrained space/slots.
As far as I know Amazon is legally closer to a market place where everyone is up their own stand (but they are required to look mostly the same) and which happens to also require you to use their payment system.
I.e. Amazon is just a proxy while the grocery store legally buys and resells the products.
I am not from the US but I think Amazon has much more market dominance than Costco. If Amazon had 20% market share nobody would mind, but they don't have real competition that comes close.
Amazon has less than 20% market share in retail overall. Remember their competitors are not just the online sellers who are pushing this antitrust angle. It’s Walmart and Target and grocery chains and CVS and Walgreens and brick and mortar department stores and so on.
I struggle with it as well because conceptually in my mind this is the same as a grocery store using customer buying data to inform itself. Grocery chains have been using private label brands to compete with name brands for years. Check your cereal aisle for the "fruit loops" in the back without a box that are ~50% cheaper than the name brand boxed real fruit loops.
I never saw this as wrong growing up. I saw this as the store offering a cheaper comparable and consumers were able to chose which they want. In fact, the grocery store also controls what is on the end cap and what is on top and bottom of each shelf.
I think the landscape is heavily skewed in favor of the dominant online retail merchant. This skew and dominance is what causes people to claim afoul behavior is going on.