How this has become a discussion about two very different shows, I can't possibly understand. (Seriously, TRUE BLOOD and THE VAMPIRE DIARIES? It's like comparing HOUSE, MD and GREY'S ANATOMY.)
I started watching this show when I was most definitely a part of the target audience, and despite my initial fear of this show being a TWILIGHT rip-off (despite the fact that the books had been written before, which yes, would make it a "Follow the leader"; mainly because Book!verse differs vastly from TV!verse), its flaws are entirely different.
THE VAMPIRE DIARIES has a protagonist-centered morality, that, when it comes down to it, isn't caused by Elena Gilbert's gentle or loveable personality (of which's existence, by now, only the Salvatores seem to be entirely certain), but the fact that she's got the special kind of boobs. Her magic hooha is infamous among fans of PNR and UF, the hypocrisy of the characters one of the most fandom-intern-critizised points of the entire show.
Despite that, we still watch it, and once you've come to the point where you hate a show with a passion, yet can't wait for the next episode, you do wonder why that is. (Or at least I do.) The heteronormativity, the lack of POCs, the annoying protagonist and love-triangle, the melodrama, the patheticly obvious loop-holes and inconsistencies. Even the beautiful and rather talented actors and actresses (and amazing music (and yes, to be fair, the few very well-written and often well-directed episodes) shouldn't be able to make up for it, right?
But in the end, the show is what the HOUSE OF NIGHT series is in the PNR bookworld. It might suck, it might be immature, sex-negative, and downright awful at times, but it's also compelling. I can't help but react to the insanities that ensue, and even though it probably isn't what the writers and creatores intended, my hatred for certain characters and the misery I feel everytime they mess an magnificent concept up beyond repair, are what keeps me coming back.
In other words, if you are looking for a well-written, sex-positive, 21st century TV-show whose writers you can trust, look somewhere else. If you want a guilty pleasure "Jesus, why do they all look so good, and wth, how is this his voice?"-experience, THE VAMPIRE DIARIES should definitely do. (Then again, shows like LOST GIRL, TEEN WOLF, and BUFFY THE VAMPIRE SLAYER are, at this point, easier to recommend with a clean conscience.)
(That isn't to say the show isn't enjoyable. Especially if you are less involved, are able to be entertained by shows despite their influence on particular people, or don't question the characters' and writers' decisions, it should be a show you might come to like.)