https://www.theguardian.com/commentisfree/2019/dec/21/law-that-helped-internet-flourish-now-undermines-democracy-section-230-john-naughton

In October 1994, an unidentified user of a bulletin board hosted by an online service provider, Prodigy.com, posted an item that was to have far-reaching consequences. The post claimed that a Long Island brokerage firm called Stratton Oakmont had committed criminal and fraudulent acts in connection with the initial public offering (IPO) of another company.

Stratton Oakmont sued Prodigy and the unidentified poster for defamation – and won. Prodigy argued that it couldn’t be held responsible for what anonymous users posted on its platform. The judge disagreed, arguing that the company was liable as the publisher of the content created by its users because it exercised editorial control over the messages on its bulletin boards in several ways and was thereby potentially liable for any and all defamatory material posted on its websites.