The approach also applies to trusting those in power. Trust judges to determine criminal sentences, and after a while it is noticed that the rich people and the white people get off easy, so there is an Augustinian outcry for mandatory sentences. After a while, it is noticed that the Rules are trapping relatively harmless people in Draconian sentences.
High schools don't want kids bringing weapons to school. So they have a discretionary policy. Some of those caught are found to have relatively harmless weapons or good excuses, so they are excused. After a while it is noticed that the rich people and the white people get off easy, so there is an Augustinian outcry for Zero Tolerance (which as Bruce Schneier has pointed out, means Zero Discretion). And so on.
Announcing a Zero Tolerance Policy and not following it (as Readercon did) is the worst of both worlds.