WARNING: SPOILERS ahead for the Dexter: Original Sin season 1 finale.
Harry makes a strong point to Brian in theDexter: Original Sinseason 1 finale that even Brian can’t help but agree with. ThroughoutDexter: Original Sinseason 1, Brian stalks Dexter and vies for his attention by killing several of his old enemies in and around Miami. It’s no coincidence that Brian’s victims turn out to be Dexter’s first assignments as a forensics intern at Miami Metro.Brian even approaches Dexter inOriginal Sinepisode 2but doesn’t reveal that he’s his long-lost brother.

TheDexter: Original Sinseason 1 finale reveals some of the more empathetic parts of Brian’s backstory and upbringing through various foster homes and institutions. After Brian nearly kills baby Deb for crying too loudly,Harry and Doris have no other choice but to hand him over to his social worker, Barb Plimpton, inOriginal Sinepisode 9. After Brian enacts his revenge against Barb, he is determined more than ever to finally reunite with Dexter but is stopped in his tracks by the wise words of Harry.
Harry Is Right, He Was The Best Thing For Dexter To Thrive, Not Brian
Brian Loves Dexter But Would Have Been A Horrible Influence On Him
Harry gives Brian a striking message during their confrontation in theOriginal Sinseason 1 finale. “Two things can be true at the same time: you’re able to hate me for good reasons and still know that I am the best thing for Dexter.” While this seems obvious, there are valid deeper points to be made aboutHarry’s decision to turn Brian overto “the system.” Some might think Dexter should have been kept with Brian, but it very likely would have ruined him.Brian accepts this in the end, writing “You’re Right"on a door in Harry’s blood.
Dexter: Original Sin Brutally Foreshadows Deb & Dexter’s Worst Moment From The OG Season 1 Finale
Dexter: Original Sin episode 9 reveals several unknown details about Brian Moser and one of his earliest encounters with his future girlfriend, Deb.
Even if Brian had been in Dexter’s life as a child, Dexter’s development would likely have been negatively influenced by him, based on Brian’s tendencies. Brian nearly killing Deb, striking Harry, and breaking a glass pane on the Morgan’s front door were all major red flags. There was simplytoo much risk for Harry to give Brian another chance. Brian could have actually killed Deb when Doris or Harry weren’t looking and encouraged Dexter to be more violent, destructive, and uncivilized.

Dexter Still Chose Harry After Reuniting With Brian In Dexter’s Original Series
Harry Did The Best He Could With Dexter & Saved Him From Brian’s Instability
In the original series,Dexter knows that he had always been better off under Harry’s guidancethan he would have been as a shadow of Brian’s darkness. This is why Dexter envisions Harry as his Dark Passenger, not Brian, in the originalDexterseries, although he briefly envisions Brian a handful of times.
While Brian is his flesh and blood, he and Dexter turn out to be very different types of monsters.

While Brian is his flesh and blood who is arguably a victim in some ways of unfortunate circumstances, he and Dexter turn out to be very different types of monsters, as evidenced by theDexter: OriginalSin season 1 finale.