Warning: SPOILERS ahead for Dexter: New Blood.
Dexter’s entire life has been shaped around Harry teaching him the code, and New Blood finally admits how wrong his father was. The original Dexter series followed the titular serial killer attempting to hide his identity from those around him while feeding his Dark Passenger’s murderous urges. At the same time, Dexter Morgan was an extremely unconventional murderer, operating under his adoptive police officer father Harry Morgan’s Code, which stipulated he could only kill deserving known murderers who had evaded the justice system.
Harry originally taught Dexter the Code as a teenager, believing his trends of killing animals as a kid would soon manifest into human victims. Under the guidance of the renowned policeman, Dexter was taught to “act normal” and hide his true self without Harry even telling Dexter why he became this way. It wasn’t until The Ice Truck Killer taunted Dexter that he realized he was found by Harry in a pool of his murdered mother’s blood as a toddler, also discovering that Harry was having an extensive affair with Dexter’s mother before her death. Even after these details about Harry and his own past came to light, Dexter continued to follow Harry’s Code and manifest his memory as his own moral conscience, a rule system he still abides by in Dexter: New Blood.
As Dexter’s original series progressed, Harry’s questionable tactics increasingly came to light, with the most damning revelation being that Harry committed suicide after seeing Dexter dismember a body. Harry couldn’t live to see the monster that he had created, which is exactly the point - Dexter didn’t have to be a murderous individual, his monstrous persona was irresponsibly molded by Harry and Dexter season 8’s Dr. Vogel. For the first time in the series, Dexter: New Blood admits that Harry teaching Dexter the Code was wrong. In New Blood episode 5’s opening scene, Dexter considers teaching his Dark Passenger-ridden son Harrison the Code. Deb responds by saying that Harry teaching Dexter the Code was “child abuse,” which proves that Dexter himself believes this since Deb is a manifestation of his own conscience.
Harry thought that was he was doing was right at the moment, but Dexter’s series proved the Code to have far more negative consequences than positive. Even if Harry was trying to protect Dexter from being institutionalized or killing innocents, he also fell short as a father to Deb. It's mentioned multiple times throughout Dexter’s original series that Deb was always chasing her father’s attention and became a cop so they could have something in common, but none of it helped because Harry was always focused on Dexter. It made Deb bitter as an adult, and part of her tragic characterization in which she always falls in love with the wrong men stems from having no male role models with moral guidelines, as both Harry and Dexter were complicit in murdering dozens of people and lying about it all her life.
The worst aspect of Harry teaching Dexter the Code is that Dexter may never have become a murderer or a sociopath without Harry’s guidance and insistence on him being a monster. Dexter tries to remind himself that he’s devoid of true emotion, empathy, and the ability to suppress his bloodthirst, but the series increasingly proves this to be false. In spite of his Dark Passenger, Dexter develops deep emotional relationships with several characters, and feels a level of empathy for Harrison and Deb that wouldn’t be possible if he was a sociopath. Dexter was never taken to see a psychologist or therapist as a child, with his diagnosis only based on what Harry and Vogel suspected. In reality, Dexter’s traits align more closely with PTSD from his mother’s murder and antisocial personality disorder - neither of which directly indicates he'll murder others. The proper route for Harry would have been to treat Dexter with therapy, whereas he instead trained Dexter to be a sociopathic killer. Had Harry done so, Dexter may have never become a killer. Dexter is finally realizing the errors of Harry’s way in New Blood, avoiding a repetition of his mistakes by instead encouraging Harrison to attend therapy for his trauma.
