I’m pretty sure this is discussed somewhere, but maybe it hasn’t been, so let’s try.
It’s (very) plausible that someone can share our moral concepts and disagree, perhaps extremely, about how they apply. Osama bin Laden doesn’t mean something different to what I do by ‘good’, he just has wild views about which kinds of actions are and aren’t good. The proof of this, if it’s needed, is that when he says “Killing Westerners is good”, he’s revealing he has different morals to me, not a different language. (Well, he has some different languages to me, but when we’re both speaking English we mean the same thing by good.)
It’s also plausible that some people can share our moral concepts and disgaree, perhaps extremely, about the conceptual connections between moral belief and action. This is just David Brink’s case of the amoralist.
It’s not plausible, or at least not to me, that someone could share our moral concepts, but differ extremely in both which things they apply to and what their connection to action is. That is, someone who said things like “Killing Westerners is good”, “Supporting democracy is bad” etc., but wasn’t at all moved to kill westerners or undermine support for democracies would, I think, mean something different to us by “good” and “bad”. Or at least so I think.
Perhaps we can imagine such a person. Imagine an amoralist in Al-Qaeda land, who goes around saying “Killing Westerners is good” and so on, but is completely unmotivated, even denies that the goodness of killing Westerners provides her with a reason to actually go and kill Westerners. Perhaps she would be just like Brink’s amoralist, and perhaps she would mean what we mean by “good”. But the case looks very marginal.
All of this does make me think that the ‘scare quotes’ response to Brink is the right one. If we can only make sense of the amoralist as expressing moral concepts when her moral expressions match up with moral orthodoxy, then it’s plausible that by “good” she just means something like “usuallly called good“.