Author is missing a big chunk of what selling retail product requires, which is shipment and delivery costs. For a $5.49 laundry detergent, the cost to ship it your may very well exceed the price of the product if you're small retailer.

At least by paying Amazon I can avoid dealing with all that. While I may pass the price to the consumer for Fulfilled-By-Amazon fees, which tends to be around $5.18 ~ $3.5 (quick google search), it's still a lot cheaper than using something like FedEx where it costs $10-12 per order.

The takeaway here is that Amazon has democratized fast and cheap delivery by building a monopoly. As the scale of things go up, the cost of operations can really go down. Think of meal prepping, when you cook food in bulk vs each meal separately, you're saving costs on power, gas and produce.

The only question is whether we can build a public benefit corporation, just like Amazon.

I'm not American, but I get free shipping on most products, as long as the order has a minimum cost and I wait a couple of days more?

This is true for other sellers too.