Executive Action

A narrator states that when President Lyndon Johnson was asked about the Kennedy Assassination and the Warren Commission report, he said he doubted the findings of the Commission. The narration ends with the mention that the segment did not run on television and was cut from a program about Johnson, at his own request.
At a gathering in June 1963, shadowy industrial, political and former US intelligence figures discuss their growing dissatisfaction with the Kennedy administration. In the plush surroundings of lead conspirator Robert Foster (Robert Ryan), he and the others try to persuade Harold Ferguson (Will Geer), a powerful oil magnate dressed in white, to back their plans for an assassination of Kennedy. He remains unconvinced, saying, "I don't like such schemes. They're only tolerable when necessary, and only permissible when they work." James Farrington (Burt Lancaster), a black ops specialist, is also among the group: He shows Ferguson and others that a careful assassination of a U.S. President can be done under certain conditions, and refers to the murders of Abraham Lincoln, James Garfield, and William McKinley as examples, and includes assassination attempts of others including Roosevelt in 1933. He calls this "executive action".
The film cuts to a desert, where a shooting team is doing target practice at a moving object. One of the shooters says they can only guarantee the operation's success by slowing down the target to 15Â miles per hour.
The lead conspirators, Farrington and Foster, discuss preparations for the assassination. Obtaining Ferguson's approval is crucial to the conspirators, although Farrington proceeds to organize two shooting teams in anticipation that Ferguson will change his mind. Ferguson, meanwhile, watches news reports and becomes highly concerned at Kennedy's increasingly "liberal" direction: action on civil rights, Nuclear Test Ban Treaty, nuclear disarmament. The deciding moment comes when he is watching an anti-Kennedy news report on the deteriorating situation in South Vietnam. It is followed by Kennedy's October 1963 decision, National Security Action Memorandum #263[2] to withdraw all US advisers from Vietnam by the end of 1965, effectively ending America's direct involvement in the Vietnam War. Ferguson calls Foster and tells him he now supports their project.
While the motives of the man in the white suit are clear, the film attempts to cast light on the murky paranoid fears of the conspirators through dialogues between Foster and Farrington. They are primarily concerned about the future of America and the security of ruling-class white people around the world. Foster forecasts the population of the world in 2000 at 7 billion, "Most of them yellow, brown or black. All hungry and all determined to love; they'll swarm out of their breeding grounds into Europe and North America." He sees victory in Vietnam as an opportunity to control the developing world and reduce its population to 550 million, adding that they can then apply the same "birth-control" methods to unwanted groups in the US: poor whites, blacks and Latinos. "I've seen the data," he emphasizes, although it is unclear whether he does it to reveal himself privy to plans known to the CIA, or to hint knowledge of even more secret information not even known to Ferguson.
The scene of the shooting is described. As news of the assassination reaches the conspirators, the film describes the effects. Farrington and his assistant discuss the fallout from the assassination, especially how to deal with the fact that Oswald has survived. Farrington contacts nightclub owner Jack Ruby. Ruby stalks and kills Oswald.
While the real assassins leave Dallas, the conspirators work to cover up the evidence. They discuss the political fallout in Washington, D.C., concerned about retribution from Robert F. Kennedy and the "believability" of the plot. Foster states that "Bobby Kennedy is not thinking as Attorney General but as a grieving brother. By the time he recovers it will be too late." The conspirators agree that people will believe in the story because "they want to believe the story." Soon after, Foster receives a call from Farrington's assistant: Farrington has died of a heart attack "at Parkland Hospital." The conspirators are now insulated from the link to the group that committed the killings.
Their work is not quite finished. A photo collage is shown of 18 material witnesses, all but two of whom, it says, died from unnatural causes within three years of the assassination. A voice-over says that an actuary of the British newspaper The Sunday Times calculated the probability that all these people who witnessed the assassination would die within that period of time to be 100,000 trillion to one.[3]

Question: Why do the conspirators agree that people will believe the story?
Answer: Because they want to believe