Aside from Stefan’s notorious ripper showcase, there’s deeper roots in his mindset in comparison to your average vampire when embracing vampiric nature. There’s several components that all drip into one big puddle of bloodthirsty impulse for Stefan in particular when he’s gone to full blown ripper state.
Why? because his existence defies the laws of nature. ( just as much as Klaus’ hybrid activation) Stefan is the doppelganger of Silas. My personal headcanon’s kind of similar to HP mythology ( for instance, how Voldemort’s soul had to be cut up into pieces for the horcruxes in order to keep his immortality) Part of the life Silas had to sacrifice for the price of immortality was his soul, and thus, Stefan’s more connected to Silas than most would assume. He’s not just some copy of Silas, he’s a reborn version of the warlock who should have died. The shadow version who should have died, being Stefan, however, interrupted the natural flow of this ancient spell. Thus, this made Stefan a glitch of some sort. Instead, he’s a sub-immortal being as well. My headcanon being, that the energy of dark magic involved with Silas’ spell is the strongest element behind Stefan’s sadistic, ripper nature. When Stefan blacks out, it’s much more than just a vampire blood drunk black out. This is also the part where dormant parts of Silas that passed unto him would trigger into vibrating at very high frequency. Silas too, was happy and content with human notions, until he suffered the pain and loss of losing his loved one. Once that happened, he grew very dangerous and malicious (according to Professor Shane at least). And this is 2000 years ago. We’re talking savage, barbaric times. This entity of wrath is primitive.
In conclusion to that, Stefan’s straddling between humanity and the enticing lifestyle of pleasure is somewhat parallel to Silas. Stefan’s extreme methods of torture, ruthless taste for destruction and infliction of misery are the darkest parts of Silas’ soul that’s passed down through the line of his lineage. It’s arguable whether we could say this is Stefan, or just a curse. I believe that the fact Stefan’s a vampire was the activation of a side he never knew. (Kind of like the Lockwoods when they kill someone and activate the werewolf curse)
FINAL ANALYSIS: ( long story short )
Basically, Stefan’s violent ripper aspect and talent for torture is fueled by the dark magic harnessed in Silas’ immortality spell. The reason he’s effected differently than other doppelgangers of Silas is because he was not meant to become immortal. He’s interrupted the balance of nature. The price of a vampire does not come cheap, especially not for a shadow of Silas who was meant to die. His insatiable lust for blood’s a result of his defying existence, haunting him in ways perhaps no other could understand. As for his extreme layers of torture, and hunting his prey? That’s because he’s a piece of Silas that’d been offered up in return of immortality. Part of Silas, and his blood is always in Stefan. When becoming a vampire, IT’S HEIGHTENED LOOL. But no really, his senseless killing, and hunting humans for sport ( ripper antics ) are due to him possessing the parts of Silas that were dark. His fury’s a sense of coping loss and pain, just as it was for Silas.
P.S. I MADE THIS SHIT UP. LOL. I DON’T CLAIM IT TO BE TRUE. IT’S MY PERSONAL THEORY BECAUSE IT MAKES SENSE TO ME