Certain opportunities to violate an injunction will only arise if the injunction exists;
some planning a murder will only confess if he expects the priest not to testify. Thus the apparent gain from violating an injunction in a single case does not actually exist on a systemic level. If prospective murders know that priests makes exception for murders, then they won’t confess to the priest and the priest will not have the opportunity to make an exception. Injunctions that seem value destructive in single instance hypotheticals can be beneficial at a systemic level.
Ethical injunctions are rules not to do something even when
you believe it's the right thing to do. (That is, you refrain "even when your brain has computed it's the right thing to do", but this will just seem like "the right thing to do".)