CiG
"On a hippie trail, head full of zombie"
The existence of a nervous system itself forms the basis of a lot of ethics. Even rabid animal rights activists acknowledge a tier of severity and importance when considering the suffering of animals, based on whether a nervous system exists in the animal and how developed it is, because the more complex a nervous system is the greater the chance to suffer is.
That doesn't get into non-physical pain though.
That doesn't get into non-physical pain though.