It would also cost however much a lawyer charges for helping to moderate every submission. Because I doubt the average WordPress blogger is familiar with all possible laws the submissions could violate. Or can make correct judgements based on precedent for things like copyright works.
Honestly though, the blogger would probably only need to pay for one hour of a lawyer's time. That lawyer would say "Turning off the comments is your best bet" and then round up to an hour for billing.
This strikes me as a solution to the problem of censorship in the same way that "just buy your medical supplies from Mexico" is a solution to US healthcare costs.
That means that you aren't going to pay $100 for a WordPress site, because allowing you to upload content without the protection of Section 230 is too much of a risk to bear for only $100.
Absent Section 230, the hosting provider could potentially be liable for anything published. They already do have to take down illegal content if they're informed about it. Section 230 predates modern social media.
If I were responsible for comments, I would do either of two things:
a) just shut down the forum, b] use a paid commenting service that would come with moderation. This means that people who would want to comment would probably pay some fee for that privilege.
Accidentally, b) is unusual for us, but a quite sustainable model. Surely more sustainable than current "show ads for free stuff", which seems to be hitting its limits.
Note that a side effect of this is that you would no longer have moderation control yourself. And how many of those paid services would exist, given the legal costs of running them?
What makes you think there wouldn't in practice be the same centralization that we see today -- one or two paid services that handle moderation for the entire Internet because only they have the lawyers necessary to do so. The only difference would be that every independent forum that didn't use them would be opening themselves up to significant legal risk.
At least right now if I set up a forum with Open Source software on a Linode server, I don't need to worry that turning off Google Captcha or avoiding a 3rd-party centralized service for my comments will get me sued.
One important difference is that the networking effect is not as big as in case of FB et al.
But yes, the general trend in maturing markets is toward some kind of oligopoly. It is, I believe, time to reactivate antitrust laws, we are well beyond the point where they should have been used.
Instead, platforms would be treated as though they had consciously decided to publish every publically-available comment/file upload/post/etc. That would probably mean manually moderating everything, and rejecting a lot of it for capricious reasons.
But honestly, I am not convinced that that would be a bad thing. It would certainly encourage more people to create their own publishing mediums, and it might help break up the titanic oligarchs that currently occupy the market.
Put it this way: I would happily give up sites like HN to remove the business model that makes mass-scale social media viable. Sites like Twitter and Facebook have inflicted unconscionable harm on our collective humanity, and they have demonstrated a complete inability to self-regulate.