Well it would certainly be more expensive than blanket immunity. Just to be clear, I think it would be terrible policy to always hold social media sites liable as publishers, just like it's bad policy to always give them immunity.
Having to argue about and decide it every single time is even worse policy. It effectively doesn't exist if you're out $50K or more every time you have to argue the ridiculously complex issue of vicarious liability on a case by case basis with slightly different facts than every other time.
Platform immunity isn't something that was invented out of thin air with Section 230. There has always been a distinction between publishers, distributors and platforms.
Generally, if you are the publisher of a work, you are liable for it.
Distributors have responsibility for material they distribute, but only if they are aware that they are distributing it.
Platforms, though, have total immunity.
Under the traditional distinction, for instance, if I am the publisher of a work, say I am a newspaper and I print and physically distribute newspapers including editorials calling Bob a pedophile, I am the one responsible for every part of the transaction and I am strictly responsible for whatever defamatory content is in it.
A distributor would be something like a news stand selling my newspapers. These are not liable unless they are actually aware of defamatory content, like for instance, a pornographic magazine calling a famous TV preacher a literal motherfucker.
A platform is usually something like a common carrier, such as a telephone company or (under Section 230) an ISP. These enjoy blanket immunity. You would not want a telephone company held liable every time someone said something defamatory to another person using a telephone and Congress, in its wisdom, decided to grant this same kind of immunity to ISPs.
Now, if there is a problem here it is, IMO, not that ISPs get blanket immunity, but that they're getting platform privileges, i.e. a near total immunity from litigation, without having platform obligations, i.e. being legally required to carry traffic for anyone. They're getting to censor and moderate (like a publisher or distributor would) but yet getting the immunity heretofore only given to common carriers.
If anything needs to be fixed, it's to force them to act like common carriers.
However, I think perhaps this kind of special regulation should be limited to extremely large corporations, perhaps by applying a First Amendment level of protection to those that deal directly with the government, like Twitter and Google are currently doing, or with a minimum market cap of something in the billions.
Getting kicked off Kiwi Farms or RetardEra or some niche site because of their weird moderation policies doesn't really harm anyone.
If you get kicked off Google, though, you're often going to end up not able to do basic shit, especially when you have stuff like jobs requiring people to use Google Docs, things requiring Two Factor Authentication from Google Authenticator, etc. Never mind employers who demand to see social media as part of the application process, forcing you to explain why you're kicked off Facebook or, if you're just a Luddite, why you refuse to even have an account there at all. Etc.
