Vampire Diaries is a vampire show that takes morality in a new creepy direction that was not explored by Twilight. To the show's credit, VD shows vampires at their worst; killing indiscriminately, brainwashing others to do their bidding or into mindless sex toys, acting in general like hedonistic monsters. The problem is the story tries to repackage them into loving, caring, boyfriends creating a warped environment where evil is forgotten or forgiven way too easily.
A large problem of the show is that it has a Kitchen Morality Sink, it just doesn't want to admit it. Nowhere is this more clear when the crux of humanity is represented by Elena, an indecisive and selectively oblivious girl with a liking for two murderous boyfriends. One of her love interests, Damon rapes and attempts to murder her friend, Caroline and later (temporarily)kills her brother. Yet she still clings to him in a sort of Tsundere type fashion, even hypocritically forgiving him when all of the harm he has done is to her friends. But don't worry, Bonnie gets back at her by falling for a sociopath that physically and mentally tortures Elena and her two love interests with gusto. Bear in mind these girls remain friends throughout all seasons of the show. Guilt by association does not exist in VD's world.
The show flimsily tries to explain the cruelty by saying that vampires can turn off their humanity. Moving aside from the inherent stupidity of reducing the complex workings and perceptions of the human psyche to on/off, the show isn't clear of how this works. Damon and Klaus are pragmatically evil yet capable of emotion, kind to their respective love interests but cruel to everyone else. Whereas, Stefan and vampire Elena turn into blood guzzling machines devoid of sanity or empathy, who need to flip their switches back to think in any higher manner.
This show wouldn't be so bad if it didn't lack the spine to be more grey. Andie, for example is Damon's brainwashed plaything for the first few seasons but Damon is never called out on it or shows remorse for his actions. Instead she is conveniently
killed off by Stefan and forgotten about thereafter. Later vampire Elena tries to snack on Bonnie. Bonnie chalks this up to her turned off humanity and is killed off only a few episodes later.
The show presents the good guys as evil as the bad, but won't acknowledge it.