The reason they're funny: Wikipedia is pretty clear on this, saying "The non-historicity of Jesus has never had traction in scholarship. Mythicism is rejected by virtually all mainstream scholars of antiquity, and has been considered a fringe theory for more than two centuries. ... In modern scholarship, the Christ myth theory is considered a fringe theory, and finds virtually no support from scholars, to the point of being addressed in footnotes or almost completely ignored due to the obvious weaknesses they espouse.". The RationalWiki pages go out of their way to reject this mainstream consensus.