This book has been engaged in a series of arguments with opponents who are disposed to challenge vigorously virtually every one of its main contentions. Let us briefly recall the main points of debate.
The basic claim upon which the book rests, namely that organisms other than human beings are morally considerable, is still by no means universally accepted, nor is it ever likely to be. The arguments which have been used to support this view are all open to counter-arguments. Thus, the argument from marginal cases, which tries to show that the characteristics that are supposed to confer moral considerability uniquely upon human beings are not possessed by all humans some of the time, or by some humans all of the time, may be resisted on the basis that moral considerability applies to all human beings in virtue of the characteristics possessed by normal, mature human beings. The claim that at least some, and probably many, other creatures do possess moral-status conferring properties may simply be refused credence, and be pigeon-holed into the category of 'anthropomorphism', thereby losing intellectual respectability. The observable fact that human beings do treat other organisms with care and consideration may be held to show that the caring moral attitude appropriate only to other human beings may 'spill over' into treatment of other things, not that those other things are really worthy of moral regard.
Even among those who are persuaded that organisms other than human beings are morally considerable, there are many who will remain unpersuaded that non-sentient organisms fall into this category. On their view such organisms are better thought of as analogous to human artefacts - complex bits of biochemical mechanism, doubtless vitally important to the health of ecosystems, and thus possessing instrumental value for organisms which do count morally, but lacking any moral status themselves. For, lacking sentience, nothing can count for them. They are thus devoid of interests, and, it is claimed, only beings possessing interests can count morally.
Even among those who have got as far as agreeing that all organisms, even the 'merely living', do possess moral considerability, there will be serious disagreements with some of the arguments of this book. Two groups come to mind. Firstly, some, within the ranks of those who will probably be well disposed to the general aims of the book, will be unhappy with the arguments which seek to justify the