Roger Scruton attempts to justify our discriminating between pigs etc. and similarly dim humans by appealing to both potential and normality:
It is in the nature of human beings that, in normal conditions, they become members of a moral community, governed by duty and protected by rights. Abnormality in this respect does not cancel membership. It merely compels us to adjust our response… It is not just that dogs and bears do not belong to the moral community. They have no potential for membership. They are not the kind of thing that can settle disputes, that can exert sovereignty over its life, that can respond to the call of duty or take responsibility on a matter of trust. Scruton, Roger (2000) Animal Rights and Wrongs, third edition (London, Metro), pp. 54-55.
Scruton concludes that, because of these differences between pigs, etc. and similarly dim humans, we are morally justified in discriminating as we do (killing and eating former; caring for the latter, etc.).
There is, I think, something intuitively deeply implausible about Scruton’s attempt to justify our current discriminatory practices. Consider the following thought experiment.
Thought experiment: a dim parallel species
Suppose that on a planet many light years from the Earth there has evolved a species that bears an uncanny resemblance to we humans. They look much like us, and indeed are physiologically and genetically very much like us. However, they are dim. They have no moral or aesthetic sense. In fact, they are no more mentally sophisticated than is the average pig. As a species, they are not, to borrow Scruton’s phrase ‘the kind of thing that can settle disputes, that can exert sovereignty over its life, that can respond to the call of duty or take responsibility on a matter of trust’.
Now imagine we are presented with two groups of individuals. The first group are orphan offspring from this other planet. They are dim because individuals belonging to that species are normally, naturally dim. The second group are terrestrial human beings: the orphan children of men and women like ourselves. But they too are dim, as dim as the extraterrestrial group, in fact. The second group’s mental impairment is due to a nuclear mishap. Their fathers were accidentally irradiated, resulting in damage to the genetic code handed down to them.
Let’s suppose these two groups are otherwise identical. Indeed, they are molecule-for-molecule duplicates of each other. The immediate cause of their dimness is in each case the same: their genetic code. However, while the two groups share the same code, they possess it for different reasons. The terrestrials possess it because they are the unfortunate victims of a recent nuclear accident. The extra-terrestrial group possesses it because of their evolutionary ancestry.
Note that while the members of the extra-terrestrial are ‘normal’ for their kind, the terrestrials are not. Human beings, under normal conditions, develop into smart, sophisticated creatures like ourselves. They are that kind of thing.
Also notice that, unlike the extraterrestrials, the terrestrials once had the potential to be smart. Had their fathers not been involved in that nuclear accident, they would have been as mentally sophisticated as ourselves. The extra-terrestrials, on the other hand, were always going to be dim. That is their nature.
Let’s now test our moral intuitions with the following question: Are we morally permitted to discriminate between these two groups? In particular, would it be wrong to kill and eat, experiment upon, etc. the second group but not the first?
If we are permitted to kill and eat, experiment upon etc. those who belong to species the normal members of which are dim, but not those who, while dim, are members of a species that, as a kind, is morally and intellectually sophisticated, then we may kill and eat, experiment upon, etc. the dim extraterrestrials, but not the dim terrestrials. If what matters, morally speaking, is what under normal conditions the members of a certain kind will become, then while we are morally obliged to extend to the dim terrestrials special treatment, we can kill and eat, experiment upon, etc. their molecularly-indistinguishable doppelgangers with impunity.
Similarly, if it is potential that counts, then while we have a special duty of care towards the terrestrials, their extra-terrestrial doppelgangers can in good conscience be put on the truck to the abattoir.
But of course this verdict is profoundly counterintuitive. How can we be justified in treating these molecule-for-molecule duplicates so very differently, simply because they differ in terms of potential and what is “normal” for their kind?
Suppose a mistake is discovered: a couple marked out for the special care centre we have designed to look after the dim humans are suddenly discovered to be of extraterrestrial origin. Would we be justified in diverting these two to the abattoir instead? Surely not.
What this thought experiment elicits (in me, at least) is the very strong intuition that the difference between the two groups in terms of both normality and potential does not justify this difference in treatment.
Indeed, what the thought experiment brings out, in me at least, is the intuition that the difference in normality and potential is simply not morally relevant.