Ars Technica:

The breadth of section 230’s immunity is historically unprecedented. While earlier legal doctrines had limited the liability of bookstores and other distributors, it hadn’t granted them the kind of total immunity that online providers now enjoy. A bookstore could still be liable if there was proof it knew it was publishing an obscene or defamatory book. By contrast, Internet providers are immune even if they know about illegal content on their sites and leave it online.

It’s hard to imagine sites like Yelp, Reddit, or Facebook existing in their current form without a law like Section 230. Yelp, for example, is regularly threatened by business owners for allegedly defamatory reviews. Section 230 allows Yelp to basically ignore these threats. Without Section 230, Yelp would need a large staff to conduct legal analysis of potentially defamatory reviews—a cost that could have prevented Yelp from getting off the ground 15 years ago.

The article quotes Eric Goldman, a professor at the Santa Clara University Law School, as saying, for better or worse, “…this rule made the modern Internet possible.”