I have said this for a very long time, but turning your humanity off in the TVD world is not changing into a a completely different person. It does not make you the same as all other vampires with their humanity off. Vampires who flipped the switch don’t all become some generic indivudal with the same wants, words, choices, ect. The switch has a different effect on everyone because the people flipping it are different in personality, dark desires, and actions.
When Isobel had it off, she compelled a man and a woman to be her minions/sexual companions and also taught them French. That’s because Isobel was a former professor, loved knowledge and was likely bisexual though the writers never said it, it was pretty obvious.
When Damon had his off, he made a lot of split decision choices, dances and drinks with a bunch of girls but keep them alive, and engaged in a faux-relationship with someone. That’s because Damon is naturally impulsive and was likely trying to fill a void for Katherine.
But when Stefan has his off, he rips people apart, takes enjoyment in watching people do things like his twister game in 3x06 and Liam Grant drinking his wife’s blood, and leaves piles of bodies/kills the people (in 3x06, 2x15, and 3x03.)
I’m not excusing or saying any of it is okay but I’m saying the switch does not turn someone into a specific type of person and it doesn’t take away all semblance of the person with their humanity.
When Stefan talks about massacring an entire village and implying that Elena will fall into that because he did, it has nothing to do with Elena or the switch.
Stefan associates all his misdeeds with an alternate identity, “The Ripper”, who is completely separate from Stefan himself and borne only of vampire nature. He projects onto Elena because of his refusal to see his actions as his own. They are because he didn’t have any humanity only even as a lot of it comes from Stefan himself as evidenced by the fact that no other vampire has exhibited similar behavior. Since everything he did was because he had his humanity off and not because of his repression and darker nature, every vampire with their humanity off must be the same.
Elena will not be like Stefan was with his humanity off because Elena and Stefan are very different. And if Elena is like Damon was with her humanity off, it is only because they are similar people.
Humanity off does not equal relinquishing every aspect of yourself. It’s more like giving up your conscience and your ability to feel as strongly. Some feelings penetrate and your personality is still partially there (albeit without the intense emotions and set morality.)