Abusers appear to be suffering from dissociation (multiple personality). At home, they are intimidating and suffocating monsters -- outdoors, they are wonderful, caring, giving, and much-admired pillars of the community. Why this duplicity?
It is only partly premeditated and intended to disguise the abuser's acts. More importantly, it reflects his inner world, where the victims are nothing but two-dimensional representations, objects, devoid of emotions and needs, or mere extensions of his self. Thus, to the abuser's mind, his quarries do not merit humane treatment, nor do they evoke empathy.
Typically, the abuser succeeds to convert the abused into his worldview. The victim -- and his victimizers -- don't realize that something is wrong with the relationship. This denial is common and all-pervasive. It permeates other spheres of the abuser's life as well. Such people are often narcissists -- steeped in grandiose fantasies, divorced from reality, besotted with their False Self, consumed by feelings of omnipotence, omniscience, entitlement, and paranoia.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/the...)