<p>Werewolves are beings, because they spend most of their time as humans. Only twelve nights a year are spent as a werewolf, with 353/354 (leap years). Besides, wolves have the instinct to hunt, kill, eat, and breed. Werewolves, however, have a more complicated mind as humans, and can decide whether or not to drink wolfsbane potions (
harrypotter.wikia.com/wiki/Wolfsbane_Potion), or not. How savage they are, their loyalties, occupations, etc... is completely their choice. Greyback decided to be savage, but it was his choice, and also his choice to join Voldemort. Professor Lupin, however, was caring and kind, drinking the wolfsbane potion and surrendering his job for other's safety.</p>