If you tell the reader it's funny, then the audience is like an audience at a stand-up comedy club and they expect you to be funny, and if you're not, they notice. Whereas if you read a regular op-ed about Israel or the family or medicine, you're not starting with the assumption that you're supposed to laugh.
Dave BarrySan Francisco leads the world in the category of Most People On The Sidewalk Holding Conversations With Purely Imaginary Companions.
Dave Barry