That's a helpful clarification. Yes, I see how tinkering with an optimal system could only do harm, although it's the system as a whole that might suffer, as the consequences would ramify.

And yes, I see how the pareto principle here is meant to be morally weak. In that case, the criticism is that in so far as this principle is offered in lieu of moral or historic assessments, the principle would act as an obfuscation.

The fact that the principle seems to be stated only by referring to "harm," though, indicates that the normativity is being swept under the rug rather than eliminated altogether. Another place where unwanted normativity seems to enter the picture is in the selection of the "initial endowment."

I wonder whether the pareto optimality principle (not the 80/20 one) might be applied to the perfect thief scenario to find that his hording of the world's resources is perfectly efficient, given some arbitrary drawing of a line that marks the initial endowment. If so, the principle itself would indeed be amoral. But if economists were to reach some consensus on where to begin the assessment of resources, such that the wealthiest one percent tend to be excused from having to redistribute more of their ill-gotten wealth, that would mean the principle is normative in practice.

I have the same criticism of psychiatry, by the way. Psychiatrists, too, want their discipline to be scientific, so they refrain from defining "mental health" or "illness" in overtly normative terms. In practice, that means they defer to social conventions and social functions, which only kicks the can of morality down the road, as it were.

It's not so easy to escape taking a moral stand. The Nazi soldiers were only "following orders." They acted efficiently relative to those orders. Likewise, Pareto's principle says that resources should be allocated efficiently, and the optimal allocation is the one in which altering it would only benefit someone at someone else's expense. There's still some conception here of a society in which no one is being harmed in a certain way, which is normative.

Honestly, though, to me the principle seems more likely just vacuous. In the perfect thief scenario, one person has everything and everyone else has nothing. Taking some of the thief's resources and giving them to others harms the thief. That might be suboptimal, depending entirely on where the initial line is drawn as to which allocation of resources is fair or natural. Or would this scenario be efficient relative to the thief's goal of starving the rest of the human population and of being the sole remaining person? Could economists stipulate to that too?

Or suppose that everyone has perfectly equal resources and wealth, say $100 each. Would that be the most efficient distribution because it's egalitarian?

"Taking" resources from someone, by definition, amounts to harming him or her, if "taking" is defined in opposition to consensual trading. So taking stuff from the thief or from anyone else harms that person. It seems, then, that any distribution of resources could be regarded as pareto optimal, when the fairness of some initial endowment of resources is stipulated since that stipulation would establish who should and shouldn't be harmed (by keeping the allotment the same or by changing it). That would be the hidden normativity.