[...] If it were a choice, it wouldn't be called a curse.
Werewolves will attack humans, but instinct and centuries of rivalry have hardwired them to hunt their prey of choice -- vampires.
Because difficult-to-control anger and aggression are common personality traits in even those werewolves who have not activated their lycanthropy, the likelihood of them losing control of their rage and inadvertently triggering their werewolf gene by accidentally killing someone is quite high; it is even speculated that the anger and aggression inherent in werewolves is intended to increase the likelihood that a werewolf will activate their lycanthropy.
However, it is possible for an untriggered werewolf to go their entire life without killing; in fact, this happens frequently enough that in some cases, a family's lycanthrope heritage will be kept a secret that will ultimately die with an ancestor, causing the knowledge of their heritage to be lost and remain unknown for generations that follow until a member takes a life and unintentionally triggers their curse; this has happened at least twice in the Lockwood Family's history.
Werewolves are also hardwired to kill vampires on sight in their wolf form, though they still hunt human prey whenever there are no vampires to kill.
One clear rule of the village was that the humans were forbidden from being around the wolves while they were transformed for their own safety, as the majority of werewolves are unable to control themselves when transformed and could easily maim or kill any non-werewolf species in their vicinity.
In Voodoo in My Blood, the origins of the Werewolf Curse and Werewolves were revealed.
A powerful witch, that was known as "The Hollow", cursed the members of her tribe that were responsible for her murder and created the Seven Werewolf Bloodlines.
Also, until their werewolf genes are activated, untriggered werewolves can be compelled by vampires just like any human, as proven when Damon Salvatore was easily able to compel away Tyler Lockwood's memories of seeing Vicki Donovan "vamped-out" before Tyler had triggered his werewolf gene.
After the gene is triggered, however, they become immune to vampire mind control.