To repeat:

The “Catholic” approach has extremely high moral standards (e.g. Be
celibate; give everything you have to the poor; love everyone), but
enforces them loosely.

The “Protestant” approach has moderate
moral standards (e.g. Don’t commit adultery; prudently give to the
deserving poor; don’t hate people who’ve never done you wrong), but
enforces them strictly.

Of course, a Catholic (or Buddhist, or atheist) could take a “Protestant” approach to ethics, and a Protestant (or Buddhist, or atheist) could take a “Catholic” approach.  “Catholic” and “Protestant,” as I’m using them, are sociological, not theological.  The question at hand is: what are the behavioral effects of the two approaches – assuming, of course, that people care about morality in the first place?

The Demandingness of the Standards

1. Moderate Protestant standards give an incentive to do the bare minimum – to go up to the edge of what’s acceptable, then stop.  Extreme Catholic standards, in contrast, give an incentive to strive for more; since it’s nearly impossible to live up to the precepts, there’s always room to narrow the gap between your behavior and your ideals.

2. Moderate Protestant standards offer a realistic prospect of achieving virtue – creating an incentive to consistently try to do right.  Extreme Catholic standards, in contrast, deny a realistic prospect of achieving virtue – creating an incentive to simply give up, to joke “Well, I’m not a saint!,” etc.  In terms of tax theory, the Protestant approach stays well to the left of the peak of the Laffer curve, while the Catholic approach almost deliberately goes far to the right of the peak.

3. Some claim that the Catholic approach is less vulnerable to the slippery slope
of moral decay.  The opposite is true.  The slippery
slope is easiest to avoid when there is a clear standard of virtue, and
anyone who falls short suffers stern rebuke.  The slippery slope is
hardest to avoid when no one lives up to your standards, and forgiveness is just an “I’m only human” away.

The Enforcement of the Standards

4. The Protestant approach gives a stronger incentive to fulfill your basic duties, by both (a) clearly identifying your duties, and (b) sternly condemning your shortcomings.  Corollary: In exceptional cases where fulfilling your basic duties is bad, the Protestant approach imposes higher counter-productive guilt.

5. The Catholic approach, in contrast, imposes moderate counter-productive guilt on virtually everyone.  After all, it frowns on even eminently defensible activities like working hard to get ahead, having sex with your spouse, or failing to love people you’ve never met.

Overall, we can imagine scenarios where Catholic standards give better incentives than Protestant standards.  But they’re pretty fanciful.  In the real world, only a tiny minority surpasses the standards of bourgeois respectability, no matter how many times they hear about the lives of the saints and hermits.  As a result, the payoff of high Catholic standards is small at best. 

Some people claim that Catholic standards are better for people with low cognitive ability.  They’re mistaken.  Kids have low cognitive ability, and how do we get them to behave?  By setting absurdly high standards, calling them all sinners, and then forgiving them for “being human”?  Of course not.  We get kids to behave by setting clear-cut, realistic standards (such as “Don’t hit people”), and then consistently punishing deviations.

What about the “Victorian” variant: Extremely high moral standards plus selective enforcement (loose for elites, stricter for the masses)?  For the elites, Victorianism just duplicates the Catholic approach.  For the masses, the effects are less clear.  Are the masses supposed to live under Catholic standards combined with Protestant enforcement?  Sounds like hell on earth.  Are the masses merely supposed to live under marginally less forgiving Catholic standards?  This gives the masses an extra incentive to avoid very bad behavior, but simultaneously raises their default level of guilt for merely existing.

In my experience, the Victorian standard’s proponents hail its flexibility: Some people need strict rules, others don’t.  But if we’re talking about the putatively dissolute masses, the Protestant approach has major advantages over the Victorian.  If people lack self-control, they need clear, livable rules, reliably enforced – not the Sermon on the Mount with an extra helping of guilt.  If we’re talking about elites, I have to ask: What is so great about giving elites the “flexibility” to commit adultery, disregard the rights of others, or vent hatred against harmless strangers?  Yes, we can construct bizarre hypotheticals where you have to cheat on your wife or rant against the Jews to save mankind.  But in real life, what is to be gained by forgiving affronts to common decency?

Perhaps I’m so Protestant that I can’t even grasp the hidden wisdom of the Catholic or Victorian approaches.  But I doubt it.  In the real world, the Catholic and Victorian approaches simply have little to recommend them.  Both would do well to reflect on the wisdom of Mark Twain: “Always do right. This will gratify some people and astonish the rest.”