It is only their specific political opponents who are acceptable targets for discrimination.
> I'm all for them deciding to use it to chuck off those who want to use it for the explicit purpose of harming others,
If your political identity is about harming others, then yes that poster thinks you should get booted from the internet. If your political identity is not about harming others then they're not talking about you or your political identity.
The person isn't being banned. Their activities are. This is legal, and always has been. Without it, someone could disrupt religious services with obscenity or blasphemy and there would be no recourse, to take just one example.
The above is entirely unlike discrimination against people on the basis of race or sex or orientation or religion because those are unchangeable characteristics.
Society is all about resolving conflicts of rights. One of those ways is that privately-owned infrastructure belongs to its owners, who get to say who gets to use it. I'm all for them deciding to use it to chuck off those who want to use it for the explicit purpose of harming others, which is fundamental to the alt-right program.
The bits and bytes of the Internet are a mishmash of private and public infrastructure, with no straightforward solution, but I'd agree that even hateful assholes deserve the ability to send and receive IP packets. But I have no problem with any private entities that refuse to help them do that.