As with Hans Fritzl in Austria, it would also have been psychologically useful to Mr Garrido and his conscience that what he did wrong - if he did do anything wrong - was kept separate and hidden from his "real" life.
We teach right and wrong to children through punishment and often anger and violence. A good child is not a moral child, it is a quiet, obedient child.
This leads us to believe that the misdemeanours, crimes and sins we commit don't count unless we get caught.
Sexually abuse a child in a secret place and then go back in the main house and wash your hands and no one knows: therefore you can feel you've done nothing wrong.
Sometimes, though, we express them because the hard wiring of our brains is not all that well planned out. (Eg The part of the brain that appears to be active during sexual arousal is close to the amygdla, which processes negative emotions, and adjacent parts of the brain tend to activate each other.) (SeeWho Are You?: 101 Ways of Seeing Yourself by Malcolm Godwin; and Rita Carter's Mapping the Mind).