Well, perhaps they are. There are obviously physical diseases. There are also mental illnesses. Why not cognitive ones, i.e., systematically dysfunctional ideas such as communism?
Disease as such cannot be understood outside the context of function, in that pathology is what happens when your telos is messed up. Rocks or stars or mountains can't be pathological because they have no purpose. More generally, nature is never wrong because it is never right.
Rather, nature is all Is, all the time. Except there is no time either. Nor even any space. Those two nebulous rascals require a perspective, and until self-aware humans happen upon the scene, there are no perspectives. We'll return to this perspective in due time.
I can see that Tallis is particularly concerned with rescuing humanism from the humanists. It goes without saying -- or saying with contempt -- that he also wants to rescue it from the religionists, but he spends very little time on them. Neuromaniacs and Darwinitwits are at least worthy of mockery. Religionists aren't even worthy, at least in this book.
Thus, he begins with a prominent atheist who absolutely savages human beings. The favorable review from Publisher's Weekly says
Humans think they are free, conscious beings, when in truth they are deluded animals.... Like the Christians of former times, scientists are caught up in the web of power; they struggle for survival and success; their view of the world is a patchwork of conventional beliefs....
He tears down institutions, especially consciousness, self, free will and morality [miraculously doing so without consciousness, self, free will, and morality!], and questions our ability to solve the problems of overpopulation and overconsumption....
Other animals do not need a purpose in life. Can we not think of the aim of life as being simply to see? This comforting question punctuates an otherwise profoundly disturbing meditation on humankind's real place in the world.
Booklist too sees no obvious flaw, let alone sickness:
Gray attacks the belief that humans are different from and superior to animals. Invoking pure Darwinism, he savages every perspective from which humans appear as anything more than a genetic accident that has produced a highly destructive species (homo rapiens) -- a species that exterminates other species at a phenomenal rate as our swelling numbers despoil the global environment. Gray explains the human refusal to confront the darker realities of our nature largely as the result of how we have consoled ourselves with the myths of Christianity and its secular offspring, humanism and utopianism.
Now, that is rich: because of Christianity, humans refuse to confront the darker realities of our nature. I'm not sure what could be darker than a primordial fall in collusion with the source of all evil (not to mention being permanently exiled from any terrestrial utopia), but we'll leave that to the side. The more interesting question is how Gray manages to elude the blade of his own condemnation. For if humanity is as monstrous as he claims, it could never produce a consciousness as angelic as his.
More cognitive sickness, from the first amazon reviewer (I don't think I could stomach wading through all 92):
If you think that you are not straw dogs that will be crushed ruthlessly by heaven [?] and earth, then you will have to read this book, among the most important philosophical books ever written.... Anybody who knows anything about human history cannot possibly disagree with Gray that we are a very violent species, although not as dangerous as the religions we have created, particularly the monotheistic religions such as Christianity.
Another devastating critique of our civilization is the way we have treated animals, of whom we are but one species but from whom we have usually tried to separate. The role of Christianity [pardon the French, but WTF?] in this endless tragedy of torture and unspeakable murder is appalling, but the consequences are even worse.
Now, that is a lot of stupid. Talk about an animal hater! Why on earth is the guy condemning human animals? Again, if you are going to revert to nature, there is only the Is. No oughts allowed. If everybody is Harvey Weinstein -- homo rapiens -- then nobody is.
While I can no doubt get a bit sanctimonious, at least I try to leaven it with a little irony. But this is a truly unhinged self-righteousness of the kind so ably described by Michael Polanyi, i.e., religious sentiment utterly detached from religion. These people like to speak with ignorant contempt of the "Old Testament God" of their malevolent imagination. In which case I would say: Here comes their New Testament, same as the Old Testament.
In the words of Jordan Peterson: dude, clean up your own house. At least Jehovah gives humans a second chance (and more). His justice is tempered by -- if not a dimension of -- his mercy. But I don't see any mercy in Gray's grim characterization.
Which is fine: if humans are as awful as he describes, then so be it. As we say -- or insist, rather -- there is no privilege higher than truth.
Wait. Truth? How did that ever find its way into a purely material cosmos? That is what you call impossible. As Tallis asks, "Was it really natural selection that eventually brought into being creatures that could see that they were naturally selected?" If so, on what basis should we believe them, or even have a category called "belief," let alone "truth"?
Speaking of which, I need some Oxygen. Dávila, arranged hierarchically from truth to truth:
He who does not doubt does not shout.
Truths are whatever any imbecile refutes.
The man does not escape from his prison of paradoxes except by means of a vertical act of faith.
The truth is the happiness of the intelligence.