Let’s talk about Dexter! The book Dexter, not the television series which is quite different. The Dexter series by author Jeff Lindsay is written from the first-person viewpoint. That is, Dexter himself is telling the story, referring to himself as ‘I’. Some books are written from the first-person viewpoint— The Hunger Games is another example— and some are from the third-person viewpoint— that is, ALL of the characters are called ‘he’ or ‘she’.
In the Dexter series, the first-person viewpoint works— in part because Dexter is a very original character and has a distinct voice. Plain-vanilla characters don’t work as first-person narrators. But there are some drawbacks.
Our narrator Dexter is different from the other characters in the story in profound ways. He is a serial killer who enjoys killing and dismembering his victims. He believes he is a sociopath, though I believe a case can be made that he has Asperger’s Syndrome and in addition has another disorder, rooted in his childhood trauma, that gave him the urge to kill. Dexter is inhabited by a secularized demon called a Dark Passenger— though he despises anyone who believes in God, non-secularized demons or any form of the supernatural other than his own Dark Passenger.
I presume that series author Jeff Lindsay is NOT a serial killer and does NOT believe serial killing is OK so long as you restrict yourself to guilty victims. But using first-person narration, he can’t let us know that. When Dexter says something that non-serial-killers would strongly disagree with, Lindsay can’t really give us a reality check using a more moral character in the story, because everything in the story is filtered through Dexter’s mind.
If a character in a Dexter novel were to cleverly refute one of Dexter’s anti-social ideas, we might never know, because with Dexter’s personality, he would be dismissive and sarcastic to even the most logical and irrefutable criticism of his warped world-view. If Lindsay had put in such passages frequently out of concern that morally uneducated readers might adopt Dexter’s anti-social ideas, he would also have had to put in Dexter’s sarcastic dismissal of them— which would make those vulnerable readers ignore them as Dexter does.
Now, I do believe a writer with a different worldview from Lindsay’s— say a devout Catholic who is very well informed on the moral teachings of the faith, and on how to present these ideas to a secularist world— could provide these reality checks in a Dexter-like series.
Such a Catholic author would have the belief that a Dexter-like character, in his secret heart, knew the natural moral law that contradicted his anti-social worldview. Such a character, when hearing sound moral reasoning, would be less likely to be confidently dismissive. And the author, with such a worldview, might simply have his Dexter-like character react to sound moral reasoning with silent rejection rather than a clever sarcastic phrase that vulnerable readers might actually believe in. (Authors who are Evangelical, LDS, or devout Jewish can also do such things.)
This is the limitation of the first person viewpoint. The author— and later the reader— is trapped in the head of the first-person narrator. Not only can you go only where the first-person narrator goes, you are restricted by that characters worldview. Whether that character is a serial killer or a saintly and devout person, this is a restriction that an author must deal with. For the inexperienced writer, using the first-person viewpoint is almost always a bad idea, likely to lead an otherwise good story-idea into a dead end.
Homework: Read the first chapter of a first-person-viewpoint novel. Take notes on how the author tells the story in this viewpoint. Then read the first chapter of a third-person-viewpoint novel. Take notes here on how the author tells the story. What things are different in the two viewpoints? What things are the same?