You could start with the basing of the case on a witness whose credibility could be called into question so easily. Go on from there.

You could say that in any case (like rape) where it was the (alleged) attackers word against the victim. In child abuse cases - you could argue that the child's credibility as a witness (i.e. being a child) is one of the main reasons they become victims.

It is certainly the case that it is one of the main reasons these victims do not tend to receive justice - in the rare occasions these abuses reach the courts.