If they didn’t act like a publisher, they wouldn’t need protection from any law since only the publisher could be sued.
Cite the case law and let me know if it’s before the law was passed.
Here’s the two most relevant cases to make this point.
Cubby v Compuserve: Compuserve couldn’t be sued because it didn’t take down any material. It was merely a distributor like a newsstand.
Stratton Oakmont v Prodigy: Prodigy took down some offensive material therefore it was a publisher and was sued for libel.
en.m.wikipedia.org
After that, they passed section 230 to protect someone like Prodigy who wanted to moderate forums but not be able to be sued for everything posted.