I listened to a lecture once, the gist of which was that many of the exceptions to our rules of evidence get created because of child molesters. A series of examples was presented to show cases were an accused molester presented a valid defence that would exclude evidence in their case only to have the court find an exception to the rule. Each time one of these cases got upheld on appeal another loophole was formed allowing otherwise inadmissable evidence to be used in future prosecutions, not only prosecutions of child molesters though, against anyone.