First, most authors try to make their stories as realistic as possible. Much of the enjoyment we get from fictional stories or movies is that we get caught up in the emotions we might have if the events were really happening. If the details clearly contradicted things we knew were true, the story would be unbelievable and we wouldn't be able to get so involved in it. If a story involved two lovers meeting on the Eiffel Tower in New York City, we would have a hard time taking it seriously, since most of us know that the Eiffel Tower is in Paris, not New York. Since it is so common for authors to include accurate background details in their stories, we are inclined to assume they are true, even though we are fully aware that the events happening to the main characters are completely fictional.
A character could, for example, quote a statistic like "32% of all murders are committed by juveniles", and we could believe that, assuming the writer was giving us a valid detail, but there is no reason that the writer couldn't simply have made the "fact" up. Perhaps a character could tell us that a certain type of gun could kill an elephant in one shot. Maybe, but the story is fictional, so there's no reason to assume the claim is true.
The movie Fargo presented a particularly interesting case. Following the opening credits, text appeared on the screen saying that the events in this movie were true. As the movie developed, the unbelievable nature of the plot made it more and more clear that it could not be true. If these wildly improbable things had actually happened, I (and most everyone else in the country) would certainly have heard about them because they were so sensational. Did the producers of the movie lie to us? Not necessarily. The movie was fictional, including the totally fictional claim that it was true! The movie was a dark comedy, and one of the jokes was this outrageous opening statement.
A lot of the problem with fiction is not simple facts but general impressions we get from what we see. If we watch or read fiction about police or detectives we are likely to find them engaged in gunfights on a regular basis. That's understandable since it makes for a more exciting story, but we shouldn't assume this is true of real police or detective work. I suspect that real police and detectives spend much of their time with paperwork and rarely, if ever, fire their guns at criminals. Since most of us are exposed to far more crime fighting in fiction than in real life, our intuition for what goes on is likely to be very unrealistic.
We can also get stereotypes of lots of other groups. While most entertainment nowadays avoids stereotyping ethnic groups, we can still be given specific impressions of certain occupations and lifestyles. Do the Godfather movies give a realistic impression of how the Mafia works? Do the Rocky movies depict what it is really like to be a boxer? Books, movies, and television give us examples of soldiers, spies, prostitutes, drug dealers, addicts, businessmen, cowboys, emergency room doctors, and many other people and professions that are likely to be far more dramatic than what we would encounter in real life.
The movie Dirty Harry depicted a dedicated police officer pursuing a diabolically evil criminal who had kidnapped a young girl, cut off her finger, and sent it to her parents as proof he had her captive and had no qualms about hurting her. The kidnapper even had himself brutally beaten up by a thug so he could accuse Harry of police brutality. Harry constantly was hampered by judicial requirements to protect the rights of people not yet convicted of crimes. The movie was clearly an argument that our country had gone too far in restricting police power. In reality such protections exist because there are sometimes policemen who, unlike Dirty Harry, are corrupt or incompetent, and few criminals are as thoroughly evil as this kidnapper, but these concerns were ignored, resulting in an emotional argument for reducing constitutional protections.
Numerous movies have portrayed large corporations as villains who pollute the environment and employ sinister means to silence those who might expose their treachery. Again, to make an emotional case, the corporations are presented in the worst possible light, and we are likely to think of this as typical of real life when in fact our knowledge is based largely on these fictional stories. While there are certainly cases of corporate wrongdoing, we have to evaluate the problem on the basis of real-life cases, not fiction.
I have seen several movies in which the NSA (National Security Agency), an intelligence agency of the U.S. Government, is the primary villain, and is involved in attempts to murder those who would reveal their nefarious activities. While it is certainly legitimate to be concerned about what is going on in an agency most of whose activities are secret, we cannot assume based on fiction that they actually would do the sorts of things portrayed in these movies.
An easy way to promote a certain point of view is to have characters that support that view be very likable and characters that are opposed to that view as despicable. The novelist and philosopher Ayn Rand used novels to promote her philosophy which she called Objectivism. In The Fountainhead her leading character Howard Roark was smart, talented, and admirable in almost every possible way, while her chief villain Ellsworth Toohey, a socialist whose viewpoint was the opposite of Rand's, was rotten in every imaginable respect. In real life, people who follow Rand's philosophy aren't always going to be so great, and socialists aren't always going to be rotten, but this fictional device is very powerful in making Rand's philosophy attractive. Many other novelists have used this method to promote a variety of other points of view. While a novel can be useful in explaining a certain philosophical or political position, we need to remember that the virtues of the characters and the results of their actions are easily manipulated by the author and tell us nothing about whether the viewpoint is a good one.
In a broad sense, almost all fiction pushes a point of view. Every story in which good triumphs over evil effectively promotes the idea that we should be good. In some cases the author may just be trying to please the reader, since people are happier if "good" triumphs, but often, particularly in stories for children, there is a serious intention to teach a moral lesson. Unfortunately the world doesn't necessarily work this way, so if we want to see the world realistically, we have to recognize that the good guys don't always win. Good behavior is helpful in many ways, such as making us better liked and keeping us out of trouble, but it doesn't help us to win the fistfight or shoot straighter or guarantee that we will be rescued in the nick of time as it so often does in fiction.
Books or movies based on true stories
The movie A Beautiful Mind was based on the true story of John Nash, a brilliant mathematician who won the Nobel Prize in economics for his work, but led a bizarre life because he was afflicted with schizophrenia. Most discussions I have seen, including an interview with Nash himself, indicate that the movie gave a generally realistic portrayal of Nash's career and his struggle with mental illness. But this was a dramatic film. Real life contains many complications that don't make the best drama, and in order to make this into a good drama, some corners had to be cut and some details changed. The movie shows Nash meeting and having conversations with people who existed only in his mind. While the movie showed him actually seeing these people, Nash himself said that he never had any visual hallucinations. The real Nash apparently spend about a decade wandering in Europe, but this was omitted from the film. A main theme of the movie was that his wife was loyal to him throughout his illness, but in fact she divorced him, although they eventually got back together. It is important to remember that although the movie was "based on a true story" and was accurate in many ways, it was not, strictly speaking, a true story. Virtually every book and movie "based on a true story" is like this.
While the best-selling novel "The Da Vinci Code" is not quite "based on a true story," it does claim at the beginning that "All descriptions of artwork, architecture, documents, and secret rituals in this novel are accurate." The story goes on to relate what is obviously a fictional plot while including a great number of historical details that, judging from public reaction, many readers assume are true. When the book was near its peak of popularity I happened to attend a debate between an evangelical Christian and a skeptic who doubted that Jesus actually ever lived. As you can well imagine, there was very little they agreed on. However they did agree on this: the history behind "The Da Vinci Code" was mostly nonsense. One crucial feature was the claim that various historical figures including Isaac Newton, Victor Hugo, and Leonardo Da Vinci had been among the leaders of a secret organization called the "Priory of Sion." Apparently this was based on a real-life hoax by a Frenchman named Pierre Plantard who fabricated the list and claimed himself as the most recent leader. It's possible that the author, Dan Brown, actually believed this and other claims to be true when he wrote the novel, but it doesn't matter. The book is fiction. The author has no obligation to stick to the truth about such historical details. He ought to be honest about his claim about artwork, architecture, documents and rituals (and as far as I know he is), but even here we should not regard a novelist as an expert we can rely on. The book was a riveting page-turner, but readers who were fascinated by the amazing historical revelations they found were unfortunately "learning" things that weren't true.
A movie which had probably been particularly misleading to people is JFK, a film by Oliver Stone about the Kennedy assassination. This is not only based on a true story, but it is a story that most Americans are familiar with. Most of the characters in the movie are real people, and most of the events are similar to real events. However it is still a fictional screenplay, most of the dialog is fictional, and at least one character is a composite of several different actual people. Facts presented in the movie are not necessarily accurate, many having been derived from claims by conspiracy theorists (who probably did believe them to be true). In the ABC news show "The Kennedy Assassination: Beyond Conspiracy", Peter Jennings described some of the other problems with the movie. While the movie claimed that Oswald was a poor shot, documents showed that he was an expert marksman. The claim that it was impossible for him to have fired the shots so rapidly were disproved by a demonstration. The idea that one of the bullets would have had to swerve to wound both Kennedy and Governor Connelly the way it did was shown to be false when the actual positions of the men in the car were carefully recreated.
Oliver Stone may or may not have believed that these details were true, but we should keep in mind that he is an expert in making enjoyable films, not an expert historian. The movie he made was no doubt far more entertaining than it would be if it stuck carefully to verifiable facts, and entertainment was his job. It is our job as responsible thinkers to recognize that a dramatic film isn't a reliable source of information.