The Communications Decency Act, passed in 1996, was, like so many other government attempts to regulate technology, something of a mess. However, it does have one bright spot: Section 230, which generally says that site providers aren't liable for content on their sites which they didn't post. Typically, this refers to things like comments and forums. For instance, if a commenter here made a libelous or otherwise defamatory statement, they're liable for it, not Techdirt. This has been held up several times in various courts, because it makes sense to target the actual source of the defamation, not the platform provider. There have been repeated efforts to narrow the scope of Section 230, but a recent decision seems to have expanded it a little bit.