Mickey and Mallory from Oliver Stone's "Natural Born Killers"
and John Doe from the classic Neo-Noir thriller "Se7en".
What's amusing about these two is even though they're inseparable, we visually learn all about Mallory, and only learn about Mickey through dialogue with a few small visuals quickly showing his past. In a flashback that takes the form of the classic TV Sitcom "I Love Lucy" (complete with a laugh track), we discover that Mallory has been constantly abused by her alcoholic Father (Rodney Dangerfield) verbally, physically, and sexually. Nobody at home stands-up to him, they just accept his abusive behavior, causing Mallory to feel alone and helpless. With Mickey, we learn a little about his past from his nightmares of being abused by both parents as well, and witnessing his Father committing suicide. On the fateful day when Mallory and Mickey meet as he delivers meat to her home, the two madly fall in love feeling salvation from the horrors they have been through. But once their love has been invaded from Mallory's Father by locking him up for stealing his car, they both completely snap and take vengeance by murdering him and his wife, only leaving her little brother alive. From this murder they feel different after ridding the people who hurt them and go on a killing spree together, treating it like a sport, as opposed to revenge on society, leaving one person alive to tell the tale of their murder. The reason why the two spread senseless violence is because they feel the world is predatory and we're all guilty of crime or sin, feeling that their crimes are no different to the common man because of that. They were born and destined to be killers from the start and are acting as fate's messenger because that is how god made them, and have evolved since they murdered Mallory's parents.
As savage and senseless as the kills they commit in the film are (like the waitress, the bicyclist), there are people they murder who are just as deserving to be locked-up as they are. It's clear that Mallory's parents deserve their fate, for their abuse and no care of her or her brother's well-being. But then you have the detective who captures them Jack Scagnetti (Tom Sizemore). Scagnetti became a detective by taking revenge on the criminal underworld for killing his Mom when he was only 8 years old, making him a hero, but he's no different to how Mickey and Mallory behave. He's vicious to criminals showing no remorse for his actions, handling them in sadistic ways that the law won't permit such as sexually abuse a defenseless Mallory in prison, and strangling a prostitute to death. Another character like Scagnetti is the warden who runs the prison containing Mickey and Mallory, Dwight McClusky (Tommy Lee Jones). He despises criminals as cold as Scagnetti does, by giving the people in his prison the same kind of senseless brutal treatment as a slave owner would, as opposed to rehabilitating them and only using force when necessary. As bad as these characters are, they cannot out-match the Award-Winning Australian News Reporter Wayne Gale (Robert Downey Jr.). One of the central themes found in the film is its satire toward the media treating crime stories as entertainment and giving criminals more attention than they deserve. Gale plays a major part in the film's theme by exploiting Mickey and Mallory's crimes to the point where audiences who watch the reports start to look at them like celebrities, as opposed to sick people who deserve to be forever locked in a cage. The terrible part is he does not care if he is glorifying the criminals and poisoning the minds of innocents. He just cares about the ratings. Even during a prison riot when people are dying, he'll keep the cameras rolling to film someone dying, or silencing someone's who's screaming in excruciating pain just to film the reunion between the film's couple. He himself starts to eventually let out his inner demons by killing a cop in a prison and reveal to his wife that he's been cheating on her. He may not have killed as many people as Mickey and Mallory have, but he's the one responsible for motivating criminal activity through his reports to a wide audience across the nation, which is much worse. And given credit where credit is due, as nonsensical and immoral as their kills are, they do show humanity inside them. Not just from their tragic past, but for Mickey feeling guilty over accidentally killing a native chief (Russell Means) who was the only person helping them out and were about to give-up their killings shortly after seeing how wielding the gun has turned to people they admire.
In "Se7en" we don't know about John's (Kevin Spacey) past as we do with Mickey and Mallory (there was at least some insight into Mickey's background), but his motive is just as clear without knowing his background before the events of the movie. All we know is that he is a die-hard Catholic based on his murders, and what is discovered in his apartment. Much like how Mickey feels that God made him to be a "natural born killer", John believed God picked him to set an example against society's tolerance towards people committing sins. Feeling that preaching God's message about sins isn't strong enough, John decides to take it to a violent extreme to make sure people will remember it. He does this by picking seven people who are guilty for committing one of the sins and kills them in horrific ways relating to their crime against god. He makes a fat man eat himself to death (eventually altering his plan by giving him the final blow to his stomach) for committing gluttony. He has a wealthy attorney to cut a pound of his flesh for greed. He forces Sloth on a drug dealing pedophile by handcuffing in bed for a full year, removing his hand, and keeping him alive while letting his body rot. Has a married man at a sex club to rape a prostitute with a bladed-strap on for his crime of lust. And disfigures a models face for pride, giving her the option to live with her ugliness or commit suicide (which she does). For the last two sins, John gets detective Mills (Brad Pitt) to kill him for his crime of envying his normal life by killing his pregnant wife to make him commit the sin of wrath that will cause him to lose his badge for good.
Despite believing he's a soldier of God, he takes pleasure in the people he harms who doesn't feel like a hypocrite seeing there to be nothing wrong with a man taking pleasure in his work. He knows that if society didn't have rules, Mills would enjoy torturing him for his crimes based on his predatory instincts. Above all, he doesn't consider the people he murders to be innocent either. He's in fact greatly disgusted that people would consider sinners to be harmless, when they're working against God's command and committing crimes that are harming society. As barbaric and unlawful his ways of handling people committing sins are some of the people he killed are indeed not innocent. The attorney lies to keep criminals out of jail for big money; the prostitute is responsible for caring diseases after selling her body to men; the man forced to kill the prostitute was committing adultery; and one of the people he kills is a criminal who has harmed children. Does that mean they deserve to die, except for the pedophile, no! They may have done wrong, but not the kind of wrong as Doe does. After all some of the people he does kill are just innocent people who made poor choices through their habits and personal outlook, like the people who were killed for gluttony and pride. Doe is right that no one is innocent because we are all sinners. However, that doesn't give him the right to murder people for it based on his beliefs. And through this whole affair he does murder someone who's not guilty of any of the sins which is Mills' Wife, who sees her as a sacrifice to complete his mission to God.
Mickey and Mallory may be portrayed as anti-heroes since we're supposed to identify with him, when with John he's purely an antagonist given how we spend the whole entire film with the two detectives. However, their motives for their kills aren't too far apart. Both feel that God made them the way they are, believing that nobody in society is innocent and deep down inside we're all savage at heart. Through these beliefs the justification for the people they kill is all for moral debate, leaving audiences thinking about society and we as a species. All it takes is a couple of cinema's most maniacal killers for getting inside our heads as they do to their victims.