From another, similar thread:
We’ve had quite a few threads on animal rights in the past. The defining distinction is the ability to argue. If someone or something is not able to argue (e.g. a young child, a senile person, a comatose person, a mentally retarded person, an insane person, etc.), then they are a legal non-entity, that is, they are not able to “stand at law”. They are incompetent. Hence, in order for them to have rights, someone who can stand at law (competent) must be willing to advocate on behalf of the incompetent individual.
However, we must be clear that, in terms of “rights”, the advocate is only ever speaking of his own rights. For example, let’s say Alice beats her dog. Let’s say that Bob decides to become a legal advocate for Alice’s dog. Bob sues Alice and claims that her beating of the dog is unlawful. The only basis on which Bob can make this claim is that he must show how Alice is violating his rights in the dog’s welfare. This means he must show that he actually has such rights. -Clayton
https://forum.freecapitalists.org/t/a-question-for-speciesists/25562