It happens in murder cases. It also happens in divorces where a perpetrator of heinous sex crimes against children, not only is free- but is "rewarded" for his crimes by gaining custody of his small, hapless victims.
The non abusing protective parent is judged guilty by default. Everyone loses- except the criminals. This, in a climate of social change that sees the public having an ever growing recognition of the pervasive scourge of child sexual abuse. The greatest loser is - our culture. We are wounding our young and experiencing the effects later in their lives, with apparently little recognition of the links between hurting developing children, and dealing with wounded adults.