Quote from : Why Does He Do That?: Inside the Minds of Angry and Controlling Men Book

If you are aware of chronic or severe mistreatment and do not speak out against it, your silence communicates implicitly that you see nothing unacceptable taking place. Abusers interpret silence as approval, or at least as forgiveness. To abused women, meanwhile, the silence means that no one will help—just what her partner wants her to believe. Anyone who chooses to quietly look the other way therefore unwittingly becomes the abuser’s ally.