It is always good to recall history. The origin of antitrust laws lies in the late 19th century, when a lot of railroad companies consolidated into a few mammoths. Back then, there were basically no regulations around the use of railroads, which were built by private capital.
Nevertheless, railroads became an important infrastructure of the nation, and the convergence of power towards just a few hands meant that the situation became untenable.
https://en.wikipedia.org/wiki/Northern_Securities_Co._v._Uni...
I can see the parallels to the digital giants of today fairly well.
Amazon (the webstore) on the other hand is getting close, and with the core business of the other FAANGs.
This is what I find so disturbing about the Parler fiasco. Every tech person I know has interacted with AWS directly at some point. Everyone any of us knows has interacted with something reliant on AWS. What's the percentage of web services that run on AWS now? It's well over a third IIRC. AWS is essentially indispensable at this point. It might very well be called a technological utility.
Moreover AWS's core market has, historically, been startups. Parler, being a startup, was in their core group of customers, dealing with a service that had effectively become ubiquitous among startups. They were an American company, with a CEO and investors and users and capital.
Being a B2B service, bordering on a technological utility, rather than a B2C online community like Facebook or Twitter, the idea of AWS banning users seems almost a category error. The idea of AWS banning an American startup would have been unthinkable to me before it happened.
EDIT: Moved some phrases around for clarity.
This may well be the legal position, but I think people are wondering whether it should be this way.
The first electricity providers were (I think, mostly) likewise completely private & free to sell or not as they pleased. But as they grew, and our dependence on their product grew, the rules changed. They are now regulated differently, and have to sell to all who pay their bills. And nobody thinks it a stain on ConEd's reputation when they are found to have been selling power to porn-studios or gun-makers (i.e. legal activities some find distasteful), nor to weed-growers or mafia-run warehouses (illegal activities, but we don't expect ConEd to hire deeply investigate every connection).
Is AWS selling something like water & electricity, a basic neutral service needed for many businesses? Or something more like a cable TV service, where they bear some responsibility for what's communicated in the channels being provided?