That's not correct, as I understand it. Section 230 says that you can't be held liable for content on your site that you did not create yourself, even if you generally moderate your content (i.e. are not just a common carrier).
But there are still laws that require you to _remove_ certain content (child porn comes to mind, but also material that infringes copyrights, etc) once you are aware of it.
Concretely, given this sequence of events:
1. You have a web site that allows people to post pictures. You moderate them some.
2. Someone who is not you or one of your employees/contractors posts child porn.
3. Before your moderators notice it, someone else sees it and reports it to the FBI.
4. You remove the child porn (based on normal moderation getting to it, or you getting notified by the person from item 3 or by the FBI).
my understanding is that Section 230 means that there is no legal liability on your part, as long as step 4 actually happens once you become aware of the content.