I think Scanlon’s main thing, his account of moral wrongness, asserts an implausible explanatory relationship. Arguably, it says something like this: morally wrong actions are those actions that would be disallowed according to a principle of public, collective disallowing (“discouraging”) that, if followed, would not result in anyone being wronged (mistreated, abused, etc.).
This is funny at least because morally wrong actions that are wrongings of persons seem to be morally wrong because the actions themselves are wrongings of persons. Why should something like [the public, collective disallowing of an action] not being a wronging of a person be relevant to the disallowed action being morally wrong?
(I’ll grant that Scanlon’s approach here makes a certain amount of sense in the context of a contractualist account of coming to some kind of ideal agreement regarding the principles specifying what to allow or disallow. But, again, the question is what this has to do with the first-order actions being morally wrong. This kind of thing is of more obvious relevance to a regime of social regulation being fair to everyone concerned in terms of the benefits and burdens provided or imposed.)
Here is a rough alternative characterization of moral wrongness and how it is connected to wrongings of persons (that, like Scanlon’s approach, counts as a broadly “Millian” approach to moral wrongness). I’m inclined to think this is a better (and the fundamentally correct) approach.
Here we go: (i) from the observer/bystander position, it is appropriate to react to one person wronging another by having impersonal moral anger, (ii) (because of this first thing, usually) it is appropriate for the observer/bystander to express this anger by objecting to the wronging (and doing other familiar things expressive of such anger) and (iii) (because of this second thing, usually) it appropriate for us (collectively) to object and do other things that amount to our publicly disallowing the wronging (type of wronging). Due to some or all of the conditions [i], [ii] or [iii] holding, wrongings of persons are morally wrong. I’d plump for [i] pretty much getting the work done.
Extending this framework a bit (and touching on a distinct criticism of Scanlon): it seems that things other than wrongings of persons are morally wrong. In particular, there is this kind of prominent case: actions that count as free-riding on the collectively-created benefits of a community. Impersonal moral anger is an appropriate response to this sort of thing. And: the community can wrong individuals (or groups), including by way of treating them unfairly, in the public allowing or disallowing of a type of action (contrast to the role this sort of thing plays in Scanlon’s view). Standards of fairness in distributions of benefits and burdens in having such a regime of allowing and disallowing (and similar collective endeavors) are important here in characterizing the moral wrongness in free-riding and an important way in which society itself can wrong individuals.