An argument form in ethics

Consider the following argument form:

1. It would be good if A were forbidden (respectively, permitted).
2. Therefore, probably, A is forbidden (respectively, permitted).

For instance, it would be bad if one were forbidden to fail to fulfill (apparent) promises made under duress. For then people could place one under duress, and force one to promise to serve them for life, and one would be obliged to keep to that. So, probably, it is permitted to break such (apparent) promises. On the other hand, it would be good if one were obliged, ceteris paribus, to fulfill promises to self, since such promises would be a useful tool for self-mastery. Therefore, probably, one is obliged to keep such promises.

As a technical point, we probably want to boost the antecedent in (1) to say not just that A is forbidden (permitted) but that it is additionally known or at least believed to be such.

Consequentialists will be friendly to a version of the argument form, assuming that there is an inference to be made from something's being believed forbidden to its being less likely to be done.

The interesting question is whether there is anything non-consequentialists can make of this argument. I think divine command theorists can. A good legislator, makes prohibitions that are good for his subjects. So divine command theorists will accept this argument form, and this counts in favor of divine command theory.

Natural law theorists will have to accept the argument form when "good" is restricted to mean "good for the agent", because of the tight link between the right and the perfective of the agent. It takes a little bit more work for natural lawyers to accept the argument form when "good" is not restricted to the agent's own good. If the agents are people, some work can be done by the fact that flourishing in a flourishing community is one of the basic goods. But to get the argument form in all generality, one might need to add theism to natural law (and a sociological matter of fact, natural lawyers overwhelmingly seem to be theists)—for theism will give one reason to think that the natures of the existent beings are in some significant degree of harmony.

What about other non-consequentialist theories? Social contract ones will probably respect this argument form. Kantian ones? Here, things are much less clear. The historical Kant's theory is theistic or at least deistic, and Kantianism plus theism or deism does make this argument form plausible: it is likely that God would arrange things such in the Kingdom of Ends that acting well is connected with flourishing. But a non-theistic Kantianism might be unable to give us good reason to think the argument form is right. That is an argument against non-theistic Kantianism.

One worry. The argument form may suffer from some circularity. After all, as Socrates taught, it's bad to do what is forbidden, simply because it is forbidden. So in evaluating what is good in (1), one needs to avoid taking the mere fact of the action's being forbidden into account.