I am not concerned here with the radical claim that personal identity, free will, and consciousness do not exist. Regardless of its merit, this position is so intuitively outlandish that nobody but a philosopher could take it seriously, and so it is unlikely to have any real-world implications, dangerous or otherwise.
Instead I am interested in the milder position that mental life has a purely material basis. The dangerous idea, then, is that Cartesian dualism is false. If what you mean by "soul" is something immaterial and immortal, something that exists independently of the brain, then souls do not exist. This is old hat for most psychologists and philosophers, the stuff of introductory lectures. But the rejection of the immaterial soul is unintuitive, unpopular, and, for some people, downright repulsive.
In the journal "First Things", Patrick Lee and Robert P. George
outline some worries from a religious perspective.
"If science did show that all human acts, including conceptual thought and free choice, are just brain processes,... it would mean that the difference between human beings and other animals is only superficial-a difference of degree rather than a difference in kind; it would mean that human beings lack any special dignity worthy of special respect. Thus, it would undermine the norms that forbid killing and eating human beings as we kill and eat chickens, or enslaving them and treating them as beasts of burden as we do horses or oxen."
The conclusions don't follow. Even if there are no souls, humans might differ from non-human animals in some other way, perhaps with regard to the capacity for language or abstract reasoning or emotional suffering. And even if there were no difference, it would hardly give us license to do terrible things to human beings. Instead, as Peter Singer and others have argued, it should make us kinder to non-human animals. If a chimpanzee turned out to possess the intelligence and emotions of a human child, for instance, most of us would agree that it would be wrong to eat, kill, or enslave it.
Still, Lee and George are right to worry that giving up on the soul means giving up on a priori distinction between humans and other creatures, something which has very real consequences. It would affect as well how we think about stem-cell research and abortion, euthenasia, cloning, and cosmetic psychopharmacology. It would have substantial implications for the legal realm — a belief in immaterial souls has led otherwise sophisticated commentators to defend a distinction between actions that we do and actions that our brains do. We are responsible only for the former, motivating the excuse that Michael Gazzaniga has called, "My brain made me do it." It has been proposed, for instance, that if a pedophile's brain shows a certain pattern of activation while contemplating sex with a child, he should not be viewed as fully responsible for his actions. When you give up on the soul, and accept that all actions correspond to brain activity, this sort of reasoning goes out the window.
The rejection of souls is more dangerous than the idea that kept us so occupied in 2005 — evolution by natural selection. The battle between evolution and creationism is important for many reasons; it is
where science takes a stand against superstition. But, like the origin of the universe, the origin of the species is an issue of great intellectual importance and little practical relevance. If everyone were to become a sophisticated Darwinian, our everyday lives would change very little. In contrast, the widespread rejection of the soul would have profound moral and legal consequences. It would also require people to rethink what happens when they die, and give up the idea (held by about 90% of Americans) that their souls will survive the death of their bodies and ascend to heaven. It is hard to get more dangerous than that.