Yes, to a point, the 'internet is free'. But you are sort of twisting the point a bit I think. Not only does it cost money to have a website in many cases, but to be close to 'free' in terms of what you can post the theoretical person you are referring to needs to run their own web server, and their own DNS server, and hopefully they don't expect to need a domain name...
Otherwise, it is not in fact free. Registrars can take your domain (look what is happening to eu domains owned by UK folx) and web hosts, are in part responsible for the content they host and can refuse to continue to do business with you.
Hell, even if you roll your own setup, the ISP you use can still choose not to do business with you, leaving your entire setup offline.
You seem to be working towards the core issue (eg. town square versus multiple substitute vendors) but you missed it while talking about cost and irrelevant details (eg. A website can be hosted without a DNS record).
As I see it, the core issue is that with enough substitutes denying business to a person/organization, the customer can effectively be denied access to “the town square”.
In the relevant case law, the “town square” is only applied when there was only a single meeting space in the town. In that case, it was a private mall. Twitter doesn’t apply as a town square on the internet because there are plenty other places to communicate on the internet, even if it is not as convenient or wide reaching. The problem lies in the case where all substitutes for a town square all block you.
The solution historically was to insist on a common carrier designation for certain utilities.
Otherwise, it is not in fact free. Registrars can take your domain (look what is happening to eu domains owned by UK folx) and web hosts, are in part responsible for the content they host and can refuse to continue to do business with you.
Hell, even if you roll your own setup, the ISP you use can still choose not to do business with you, leaving your entire setup offline.