That the efficacy of the Sacraments doesn’t depend on the holiness of the priest is just about the greatest thing ever. No other profession has this kind of profound disconnect between the agent’s ability and the effects of his actions. Consider: whether you live or die depends on the skill of the doctor. Whether you are found guilty or innocent depends on the skill of the lawyer. But whether you receive the Grace of God from a priest doesn’t depend one whit on him being a good priest, only that he is a priest. That is what demands respect.
Of course we should call out clergy who are not living up to their vocation to be in persona Christi. Their evil actions demand no respect, but their ontological status certainly does. We may be tempted to think “I will speak to that priest as if he were Christ as soon as he starts acting more Christlike!” I would offer that the most critical time to see Christ in others is precisely that point when they have failed to see Him in themselves.