> Using your example let's say that no other company can sell diapers online. That means for consumers that either don't want to or can't buy from Amazon, they are materially hurt from the lack of competition.

If a group of consumers can't or don't want to shop at Amazon, then they've just created a niche in the market (be it due to geography or anti-Amazon sentiment), that would create a demand for a diaper store that would serve those customers, because, by definition, they have just outcompeted Amazon by being more available or appealing to the consumers.

> The only possible argument here is that it's possible to have a singular organization that provides everything better than a diverse competitive market could. Neither history nor theory supports this thesis and the secondary effect on economies and political power compounds the downsides.

I believe history shows that as long as said singular organization it keeps providing everything, it will prevail (in everything). The moment it stops, it collapses and new players come in its place. This is, of course, as long as state doesn't decide to bail it out like it historically did in several heavily regulated industries, which are hard to enter partially because of said regulations. Consumers are rarely hurt in the process, as long as you let the big company take the fall, and let the new better companies grow its place once it stops delivering. If you regulate something like Search, to Google it's just extra operational costs, but as a side effect, Google becomes too big to fall, because no one else can really step in its boots anymore and enter the market.