For two astonishing hours on Wednesday night, the PBS network in the U.S. broadcast a new film devoted entirely to religious propaganda, Muhammad: Legacy of a Prophet. Innocent viewers received no warning. The listings implied that we were to see a documentary, which usually means a mixture of fact and argument, the sort of thing PBS broadcasts on Iraq, Benjamin Franklin, or for that matter, Jesus Christ. But most of those who sat through Muhammad: Legacy of a Prophet must have realized eventually that this was no documentary. It was an Islamic sermon on film. PBS documentaries often display grievous...