Some Anvils Need to Be Dropped/Radio

Adventures in Odyssey does this every episode rather well. In fact, they've perfected it.
In the Superman radio show of the 40s, there is a fairly famous serial in which Superman takes on an expy for the Ku Klux Klan, complete with their real-life ranks and secret phrases. This radio show was used to expose the Ku Klux Klan what it really was; a terrorist organization that had to be disbanded ASAP. It even went and revealed the identities of individual Klansmen, hoping to induce good-hearted people to go after the Klansmen themselves and harass them until they were too broken to so much as spit upon a black man. It Worked. Suddenly, the Ku Klux Klan was forced to disband in the face of overwhelming shame, public ridicule, and vicious assaults on its members. They've never managed to regain their former power since then.
On the radio show The Saint, during the episode "Author of Murder", Vincent Price (the voice of Simon Templar) delivered an unsubtle yet eloquent message on the evils of prejudice and racism.