That, quite simply, is the ethical basis for not extending to animals the same rights as we demand for other humans. That is to say, they have no possible way of understanding, let alone reciprocating. And of course the fundamental reason we want such rights extended to all humans, is that we reason that it is the best way of ensuring that we personally will enjoy such rights. Humans are capable of grasping the concept of reciprocal rights.
Animals can't and won't reciprocate. The whole notion of extending universal human rights to animals is preposterous.
[WS:] I fundamentally disagree with it. You are making a positive statement based on the lack of knowledge, basically an argument of the kind "I have not observed X, therefore X does not exist." I do not know what your concept of reciprocity is, but I certainly observed a lot of animal behavior that fits my concept of reciprocity, which is responding with an action similar in kind to once received from another being.
More importantly, I fundamentally disagree with the utilitarian concept of ethics that you seem to espouse, namely that people reciprocate and grant other people rights solely because this has the utility of obtaining the same for themselves. I am pretty sure that it is not how most people think - most people do what they think is right, not what they think will maximize their safety, convenience or utility.
The pitfall of this argument is that the normative principle in question does not hold in non-reciprocity situations. If one can ensure that one is not paid back in kind for one's actions, one is not obliged to extend the notion of rights to anyone. The victor or the jailer does not have to extend any right to the conquered or imprisoned people, because they are prevented from reciprocating. Why should he? Whether those subjugates are actual animals or "tier-menschen" to borrow from Nazi terminology, they are prevented from reciprocating by force, so they do not deserve any rights.
I have a rather strong distaste toward utilitarian ethics (not as much as toward religion, but close,) because it is an ethics of convenience that can justify almost anything. In the extreme case, it is the ethics of concentration camps. But even more importantly, it is the ethics that makes the individual rather than something greater than individuals (e.g. collective or the universe) the center of ethical gravity. In that respect, it is the ethics of capitalism.
As I already said, I also believe this concept of ethic is antithetical to what most people think. Most people follow deontological ethics of doing what is right, which is based on the concept of duty. The notion of duty is innate and universal - virtually people have it, albeit the actual contents varies from culture to culture. I believe, however, that the duty to reciprocate is pretty universal too.
>From that point of view, it is possible to extent rights to anyone or
anything on the grounds that this is a right thing to do (i.e. one has the
duty to do so.). I extend the concept of rights to animals not because they
can reciprocate, but because it is an ethical thing to do. If I did not do,
it would say something negative about me, even if animals could not
reciprocate (even though I think they can).
Wojtek