If Mackie's epistemological argument from queerness is correct, then Mackie harbours an intuition that is equally mysterious to the one he rejects. For this reason, someone may reject my criticism of Mackie because it is unfair to ascribe such an intuition to him.
It should be clear from his work that Mackie is an empiricist. Thus, he wants to deny (1) that there are such things as objective values that are not grounded in experience, and (2) even if there were such things as objective values, we could not know them because we do not have some queer form of moral intuition. These are two consequences of his epistemological argument.
If Mackie is correct that we have no special intuition that allows us to access objective values, then he must be able to individuate perception from any other form of intuition that is not perception. This would suggest that he has good command of what we can perceive and not perceive.
Knowing the boundary between what we can and cannot perceive, however, assumes that you are able to see beyond the boundary to know what is not perceivable. Good command of perception invokes knowledge of perception. On Mackie's empiricism, we are able to tell that bacteria are perceivable with the use of a microscope, distant galaxies are perceivable with the use of a telescope, and medium-sized objects are perceivable using only the naked eye. These would all be perceivable, according to his view.
Mackie's judgment that objective values are not a matter of perception doesn't come from not being able to experience them in the way we can perceive distant galaxies, bacteria, or medium-sized objects. No instrument may help us perceive objective moral values. Moral values lie beyond what is perceivable and open to inspection. Granted, we may be able to perceive the traces of objective moral values in what actions we have deemed to be morally correct or incorrect in accordance with principles that guide action. Yet, that kind of assessment wouldn't amount to objective moral values. Those are still not observable.
We don't seem to have good enough command of perception to determine what lies on the other side of perceivable. We can only say that objective moral values are not observable in the way that medium-sized dry goods are. They are not tables or chairs, for example. But, then again, we shouldn't expect objective moral values to be so perceivable. We can mistakenly think that we see a round tower in the distance (it's actually square), but it would seem bizarre to say the same of objective moral values. "I can't see the moral value in the distance." That we cannot talk of objective moral values in the same way we speak of observable things suggests that they are not like familiar objects. So, we seem to have a reason to think that just because we cannot perceive objective values doesn't mean that they do not exist or that we cannot intuit them.
Mackie's argument wants to say that things that are objective cannot have any influence on us. If they have no influence on us - particularly through the senses - then we have no reason to think there are such things. This seems to work very well against objective values. If we haven't seen 'em, then they're not there. However, I have raised a sceptical concern against Mackie's argument. Objective moral values aren't like objects or events. That they're not like them means that one may be perceivable and others may not. Objective moral values may be among those things that aren't directly observable.
This argument, however, works equally well against Mackie because he has presumed that nothing other than experience guides our ethical thinking. Since we cannot perceive objective values, they cannot guide our ethical thinking. The empiricism Mackie invokes is an objective concept. If empiricism is an objective concept, then he defeats himself. There is nothing that can be objective because that would mean it is beyond our perceptual capacity.