Ozzie, I see your point. It's obvious that the confessing party is either guilty of the sin being confessed or they're guilty of lying. If they are lying it is a serious lie (slander) against the other party. The two witnesses rule is designed to protect an innocent person who has been falsely accused.
In a situation where the accused but denying party has been accused of a sin that is also a crime (i.e. child abuse, etc.) then the matter should be referred to the police who will hopefully determine the truth and bring charges if necessary. If the accused party is found guilty of the Sin/Crime in a court of law then the congregation can also deal with them in an appropriate fashion.
Unrepentant sinners (gross sin) should be disfellowshipped (this is scriptural). Someone(s) must take this action, so I suppose that is why JCs exist. The problem is that the men on JCs are not held accountable when they deal with matters in a corrupt way. In fact, I personally will never trust the WT JC process until they figure out how to adaquately police themselves (like the legal and medical professions).
FM