??
You wrote: "It teaches people to think what they're told to think". Your argument is that JFK's public execution was a message to teach people what they should think. "It" being his public assassination.
What did JFK think or say or do so that he needed to be publicly silenced or kept from the "people" so that they wouldn't think differently? In other words, publicly killing JFK sent what message to the people about their thinking? They couldn't think what? What was JFK helping make them think?
And King was assassinated in 1968. It wasn't public; there's no film, very few people were around him when he was shot. And by 1968 his goals were met; it was too late to "undo" the civil rights revolution that he started. Killing him in 1968 was too late if he needed to be silenced for his "thinking" differently.