According to a family of “contractualist” views of morally wrong action pioneered by Thomas Scanlon (in the narrow sense of ‘wrong’ that entails wronging someone and the victim having claims against one not to perform the action — “what we owe to each other”), what makes an action wrong is that it cannot be justified to others. The appeal of this sort of view is at least twofold. First, it specifies a very intuitive way in which actions are made wrong by the reasons (interests, well-being) of others. Second, it occupies a theoretically appealing “third way” between the utilitarian take on morally wrong action as not-welfare-optimific (or indirectly some function of this) and various Kantian (and related) positions according to which morally wrong actions are a type of action that reason itself forbids us (or that otherwise are irrational or violate rational requirements). The specific formulation of contractualism that Scanlon defends is a bit different (and of necessity more complicated) from the core idea just expressed, but the core idea of justifiability-to-others captures the essence.
I suspect that action not being justifiable to others, or at least not being justifiable to them in a certain moral way, hits close to the mark, if not precisely on the mark, of what makes an action morally wrong. I suspect that something like this is true: the essential constitutive kernel of the wrongness is actions being objectionable to affected parties or patients — and that this is what (a certain kind of) justifiability-to-others is concerned with, leaving inability to justify to others as a kind of criterion for wrong action (and also as an ideal for consensus regarding what is objectionable and unobjectionable, wrong and right, in contexts of rational and reasonable contention). This, I believe, suggests the right directions and challenges for an account of what moral wrongness is (and of which general sorts of actions are right and wrong and why).
My task here is modest: saying some important things about what it is to justify actions to others and, in doing this, distinguish the different roles for actions being objectionable and unjustifiable (to the affected party or patient) and, in doing so, provide a strong, basic reason for thinking that contractualism (or any kind of contractualism that takes unjustifiability-to-others as constitutive of wrongness) is false.
I might attempt to justify a proposition (or belief) to you. I take that to work like this: I am providing you with reasons or evidence for you to take up and use in your own, private rationalizing process. And I am hoping that, on the basis of the reasons that I provide, you will come to believe the proposition. Maybe I want to convince you that Worchester is farther from Providence than Boston.
But something different is going on when I try to justify my action to you. If we are building a house together, I might try to justify to you my using screws instead of nails to attach the wall studs. My aim here is to get you to accept my action (or at least acquiesce in or not reject it) on the basis of relevant reasons that I articulate to you (like that using screws results in an adequate amount of structural strength for the wall). My aim is not (or not simply) to get you to believe some proposition (though perhaps the route to rationalizing your acceptance would be via believing that using screws is acceptable relative to what having an adequately sound and strong wall requires or some such).
Now consider a moral case: I am trying to justify to you (say, after the fact) my telling you a small lie to avoid us having (what I regard as) a pointless argument. I might give you reasons like “this lie actually benefits you” or “this lie was not performed out of negligent, self-indulgent or malicious intent.” Whether or not, if we filled in some more details, my attempt at justification would or should succeed, what I am trying to get you to do is this: not object to my action (on familiar moral grounds concerning how one is being treated).
How would the objection-producing rationalizing (that I am wanting you not to engage in and appropriately not given the reasons or evidence that I present) go for you? Something like this: you’re representing the action as being of some salient descriptive type, you’re judging that because of this my action warrants resentment (or moral anger) and lodging an objection against me, you’re experiencing resentment and objecting. (Most often, such reasoning or rational response is super-quick and perhaps unconscious: often, one experiences resentment or moral anger in a way that seems automatic or almost reflexive. Typically, one does not experience the movement from explicit belief in attitude-appropriateness to having the attitude.)
We might, then, sum up what I am doing in this moral scenario as follows: I’m trying to convince you that my action (my lie) is unobjectionable in the specific sense of not warranting resentment (or moral anger) and hence objection. My action might be unobjectionable even if I’m not able to justify it to you. And I might be able to justify it to you even if it is objectionable. This is analogous to the distinction between truth and justification in private epistemic justification. Meeting rational or justificatory standards, especially idealized ones, reliably meets the correctness standards, but it need not do so in any given case and the correctness standards are independent of the justificatory standards. The correctness standard here is the standard for resenting something that someone else does (in one’s role as patient or affected party).
But if this is right — and if an action being objectionable (or “patient-objectionable”) in this sense is necessary for it being wrong — then the wrongness of an action cannot be constituted by it being unjustifiable to others. This would be analogous to saying that truth is constituted by justification (or justification under ideal conditions). So: the wrongness of my negligently stepping on your toe might be (partially) constituted by the normative correctness standards internal to resentment, but it is not constituted by this action not being justifiable to you (or to anyone in your position). This leaves many of the normative features of wrongness unexplained: (i) appropriate observer attitude and behavior reaction, (ii) appropriate agent attitude and behavior reaction to her patient-objectionable action and to patient — and observer — complaint or objection, (iii) the sorts of reasons that go into what actions we collectively appropriately or best allow or disallow and (iv) how and why all of these distinct normative elements, plus the fundamental normative element of patient-objectionability, hang together to form one unified normative feature. Providing such explanation is the path not taken by Scanlonian contractualism. It is a different path starting from the common idea that the wrongness of actions is very closely tied to justified or appropriate resentment, complaint, objection, rejection, etc.