If animals have rights, shouldn't they have responsibilities? For example, dolphins have been known to kill porpoises, or even other dolphins, for fun. Do not the dolphins deserve the death penalty for these heinous actions?
You might argue that dolphins are not developed enough to have moral responsibility. But dolphins are not developed enough to have morality, why should they be developed enough to have rights?
Most animals rights activists (call them ARA's) assert that a humans right to life and well-being comes not simply from being human (that would be speciesist.) Instead, they assert that our rights come from from our functionality or development. Part of our development includes a moral dimension. So by the standards of ARA's, any agent with rights also has responsibilities.
I doubt the PETA would approve of me stabbing a porpoise to death. Why aren't dolphins held to the same standard?