To argue that we humans are capable of complex multifarious thought and feeling, whereas the sheep's perception is probably limited by lowly sheepish perceptions, is no more to the point than if I were to slaughter and eat you on the grounds that I am a sophisticated personality able to enjoy Mozart, formal logic and cannibalism, whereas your imaginative world seems confined to True Romances and tinned spaghetti.
I don't hold animals superior or even equal to humans. The whole case for behaving decently to animals rests on the fact that we are the superior species. We are the species uniquely capable of imagination, rationality, and moral choice - and that is precisely why we are under an obligation to recognize and respect the rights of animals.
The person who kills for fun is announcing that, could he get away with it, he'd kill you for fun. Your...life may be of no consequence to anyone else but is invaluable to you because it's the only one you've got. Exactly the same is true of each individual deer, hare, rabbit, fox, fish, pheasant and butterfly. Humans should enjoy their own lives, not taking others'.
I don't myself believe that, even when we fulfill our minimum obligations not to cause pain, we have the right to kill animals. I know I would not have the right to kill you, however painlessly, just because I liked your flavour, and I am not in a position to judge that your life is worth more to you than the animal's to it.
To us it seems incredible that the Greek philosophers should have scanned so deeply into right and wrong and yet never noticed the immorality of slavery. Perhaps 3000 years from now it will seem equally incredible that we do not notice the immorality of our own oppression of animals.
In a sense, the first (if not necessarily the prime) function of a novelist, of ANY artist, is to entertain. If the poem, painting, play or novel does not immediately engage one's surface interest then it has failed. Whatever else it may or may not be, art is also entertainment. Bad art fails to entertain. Good art does something in addition.