The point is they can't do whatever they want, just like Google/FB/Amazon actually can't do whatever they want.
They can only do it if it's the will of the majority of their customers, employees and shareholders. Jack Dorsey or Jeff Bezos can't make decisions like this unilaterally without the support of all those parties.
I'm not sure about Twitter, but Bezos is the majority shareholder at Amazon and if he really wanted to, could make the decision to ban anyone he wants and nobody would legally be able to stop him, will of the employees/shareholders/public be damned.
Of course he made a statement that made himself sound courageous, but it was the easiest decision ever and a PR move lol.
If AT&T terminates customers’ access to websites, customers will go to Verizon etc.
If all providers blocked access, they must have a good reason.
I'm not sure if you're familiar with the ISP market in the US, but the point here is that there are many areas in which customers cannot switch to another ISP. If AT&T were to block websites, those customers would have zero ability to access them. Hence the "some companies are too big and influential" bit.
For curiosity I registered and took a look, it’s disgusting and I absolutely support it being obliterated.
I also think that the real world isn’t that hypothetical and there are a lot of rights and wrongs. You shouldn’t give these racists the same freedom.
But if a website is willingly violating terms of service defined by the provider (hosting child pornography, spreading racism etc), I support the IPS to block access or whatever.
The fact that some users have no alternative is another problem.