CDNs are not the only way to provide protection against DDOS, they're a packaged offering combining multiple technologies but there's nothing preventing you from running geolocated servers, on multiple providers, with ddos mitigation you buy/build yourself. Blocking at the DNS layer (through multi-party action I guess) is going to be an insurmountable hurdle. Wanting cloudflare or any other company to offer you prerolled infrastructure as a right is ludicrous. This distinction is anything but arbitrary.
Maybe not strictly insurmountable. But building your own massively distributed infrastructure capable of resisting DDOS attacks is expensive. Perhaps prohibitively so, depending on the size of your budget.
You could just as easily argue that since DNS blocks can technically be overcome by directing users to a specific IP address, or by using an alternate name server infrastructure like Namecoin, that DNS isn't critical.
In my opinion, the distinction is rather blurry.
Is the internet not a "knowledge/information utility"? Do CDNs not provide critical protection against DDOS attacks? How then does denying service not "prevent 8chan from delivering it's message"?