Social media have been pushing back against being categorized as publishers. This is understandable, like everyone else, they want to maximize their income and minimize their responsibilities. Nobody wants extra work. Seems like they are clinging to the notion that they are carriers the way the phone companies are (were). It has been pretty obvious to me that they are neither strictly publisher nor carrier, they are new and different public media and regulation has not kept up with the way the environment has evolved. I think it's a mistake to try to shoehorn them into existing categories. To some extent, these changes have also affected traditional phone carriers too. You can now send text messages simultaneously to many recipients, that's not exactly a private phone call anymore.
The exemption to law suits was granted to the social media companies in the early days of their creation to facilitate their expansion. It was a way to avoid bogging down a new industry that was just getting going and that was deemed to be important to the wider culture. This was an explicit choice at the time and has not been revisited. (I linked to a podcast interview a few months ago in which an expert in the field told about that development history. I cannot find it at the moment.)
Alan keeps describing Facebook's and Twitter's actions as censorship of political ideas. In this instance, that's nonsense. Trump was not just voicing a viewpoint that they disagreed with. Those platforms are full of different opinions on numerous subjects. In any case, Trump has access to many distribution channels for his thoughts, as Pres, so just because these two in question tossed him out doesn't bother me that much. Given how he has been spewing out conspiracy nonsense for years now, they should have done it sooner to bring this all to a head. But I can see how they could behave like that one day. It might too tempting for them not to. Would they censure criticism of one of their largest customers someday? Have they already? I don't know. If they were media, in the old sense, there would be a separation between editorial and advertisement, or there was in the old days when there were hundreds of these entities competing in the marketplace. We don't have that anymore.
The code has a bug and it needs to be fixed, and it's not a technology problem.