Humans have a right to luxury, provided they gain it rightfully through work, that animals do not have because we have the capacity to enjoy more of life than they can. For example, one of Leonardo Da Vinci's paintings or Mozart's arias will mean nothing to a pig or falcon, but they might be very important to a human individual. Because of our mental capacity, we can experience pleasures far above that which an animal can. And animal rights activists must recognize this much because it would be absurd to argue that pigs deserve to be housed in fully urbanized apartments just as humans do. It would also be absurd to argue that a human child should live the way pigs do on a farm since it would keep him alive and well-fed.
Human existence is much more than just survival.
Our cognitive abilities have opened a new world of higher pleasures to us and we have a right to them. We've seen that suffering is not the right word to describe it, and I will argue that evolution has guaranteed that life be full of necessary suffering. Life feeds on itself to survive. But for something to continue living, something else has to die. If omnivores slaughter animals, then vegetarians massacre plants.