My two pennies:
Moral 'rights', as many before have said, are a made up concept. Further, I don't think they are a very useful concept. Anyone can claim a right to anything. Worse, when 'rights' are used in a moral system, there seems to be a tendency to conjure up arbitrary qualities one must possess in order to be said to have rights - like 'maleness', 'whiteness' or 'human-ness'. Ughh.
Instead, I prefer to think in terms of interests. For example, I have an interest in being alive, in not feeling pain, etc. Interests can be weighed against one another, for example, my interest in getting rid of someone who irritates me is clearly less than their interest in being alive. If you are very bored and are interested in my moral position, see the utilitarianism thread.
Just have to comment on this, though:
fredjones wrote:In this sense, I don't think it is immoral to keep hens caged, since the hen is not a sentient being. I admit that they feel stimulus, but I do not think that it is a defensible position to say that they suffer. If the hen were sentient (sentient = capacity for suffering) then it would be immoral to use them like we do. As it stands, chickens do not have the mental capacity to know what suffering is. I contend that we have domesticated them to the point that they have the same rights as insects, which almost no one defends in these kinds of debates. (sorry, a little tangent there). If you can prove that chickens suffer more than insects, then I may change my mind.
What do you mean 'do not have the mental capacity to know what suffering is'? If you mean 'do not feel pain', then I think you are just wrong. To my knowledge, scientific research on the subject has turned up fairly conclusive evidence that animals such as chickens, fish, etc. do feel pain. Would such research change your mind?
I don't know if insects feel pain, perhaps research is being done on it. By the way, can you prove that you suffer more than insects? Your 'rights' may depend on it...