Defamation for starters. See Neibich v. Reddit and Berger v. Reddit. So far section 230 has shielded them from much of these but the law has been targeted over the last couple years. So far the Supreme Court hasn’t addressed questions on the scope of section 230. I’m guessing the thinking goes if section 230 scope is narrowed and moderators are on the company payroll that could move them from a content provider (not liable) to more of a newspaper publishing articles (liable).