There is a growing movement for the bestowing certain non-human species with legal rights of a person. What might be some of the most significant or important philosophical arguments in favor of such a policy?
My understanding of the problem is that the growing body of scientific evidence about non-human intelligence and social development of animals is pushing the scales towards granting some animals some rights until now reserved only to humans (for example, banning the catching, confining or hunting of cetaceans). Moreover, these bans would not be put in place for ethical reasons only (for the cetaceans' welfare) but because of the cetaceans' status (== cetaceans are kind of like us, so we can't do to them what we wouldn't do to humans). One could say that it's still an ethical problem, but at least an already solved ethical problem (we have almost universally decided that human slavery is wrong some time ago).
I think this is a more narrow version of the argument ("they're like us, so we have to treat them like us") as opposed to the more broader one ("they can feel pain, so we can't hurt them").