<p>The problem comes not with clear opinions, but when the page starts including factual statements that are based on rumors–if these aren’t true, then it can be libel. The line can be easy to cross. “The teacher is lousy” is opinion. “The teacher sleeps in class” is factual, and libelous if untrue. And if the page allows comments from other people, the page host is probably “publishing” those comments, and might be liable for them.</p>