Fear and anger both produce catecholamines. Such as adrenaline. Adrenaline rush is somewhat addictive. Adrenaline has adrenochrome as a by-product: yes, being hyperemotional will give you that same rush supposed to come from vampirism. The adrenochrome doesn't last, but it may play a part in further brain processes. So Zuby is right on, people like their fear, and anger, just like a drug, because it causes a drug effect.