The sites you listed are notorious bad actors but they at least have a degree of moderation.
Imagine hypothetically that you have website about the plight of the Uyghurs and Amazon was a Chinese business.
Amazon's behavior revealed they are not above terminating service for businesses. I can imagine a world where they become emboldened and attempt to deny service to parties they don't like.
Perhaps you're hosted on AwS and they make an offer to acquire your business. Can they shut you off or raise your prices if you reject their offer? Can they escape antitrust scrutiny and use this as a strategy to low ball you?
I view the response to Parler as an operational test of the death star.
We have less and less power the larger these giants become.
As a society we make value judgements all the time. I think most people were in favor of shutting down parler. Most people are not in favor of letting AWS deny you service if you don't accept their aquisition offer and the response will be different.
I don't think we should force amazon to host ISIS' terrorist planning
What percentage of Parler users were advocating or planning for violent protest?
Also note that this stuff happens on Facebook, Twitter, and other social networks all the time, and yet they're still online.
These are really messy gray areas, and the choices we're making will set precedents for our future.
There are so many potential responses by both the host and the service/platform. You can ask the network to deal with it (as they did with Parler), you can involve the FBI, invoke lawsuits... I don't think deplatforming is the second course of action to take when politely asking doesn't work out.
Was it even Amazon's prerogative to ask for content removal? It might be in their TOS, but what would the DOJ say?
Unless the FBI or CIA says it needs to go, I don't think it's Amazon's call. That should be our bar.
Social networks should be able to set their own rules and operate within the laws of the United States. Web hosts shouldn't meddle.