Create an "Opinion" section and separate all Op Ed pieces from "News" sections.
Stop posting Op Ed pieces as "news".
Raymond Schreffler commented
I agree 100%. We have to many people out there who take opinion articles as if they were actually real news stories. You also need to label articles that are clearly someones opinion even when the writer themselves does not inform the reader that it is the writers opinion. As soon as you see a writer calling a politician an inappropriate name or bad mouthing them you know it is an opinion piece as a real journalist would not allow there bias into a true news story.