Certain kinds of people or not, he is now a known serial killer with a huge list of murders on his hands. Not to mention, his actions have led to the deaths of innocent people which is now, also, known to Deb. He creates destruction that directly effects Deb everywhere she goes. She has gone through living hell because of Dexter and she now knows it's ALL because of him. All of the trauma that Deb has gone through in 8 seasons has been because of Dexter. She almost got killed, the love of her life did get killed, she found out Dexter almost killed her, Deb knows Dexter's actions directly led to the murder of her nephew's mother, and Christ, the list goes on. Not to mention her built up over the seasons belief in her job and her dedication to the law and doing it the right away. She's a cop's cop.
So all of this is now in the air, right out in the open, in front of her face. There is no way her character doesn't turn him in if this was projected to real life. Oh, let's throw in the fact that Dexter has revealed to her that her own father has been lying to her since she was a child. Deb has all ready shown she is an emotionally unstable person and when extremely flustered she acts wildly and with abandon. But now, her whole life has basically been exposed as a lie and a world of torture and living hell and it's all because of Dexter...and she thinks logically about all of this going on now? She reacts calm and coolly. Bull. Fucking. Shit. Don't buy it.