Your argument against killing animals fails on its own grounds. Animals kill other animals all the time, without regard to some "cognitive" scale. Is it immoral for a lion to kill a gazelle? Or a honey badger to kill a cobra? No, because honey badger don't give a ****. Animals have no concept of morality or self-awareness nor any concept of what "intelligence" is, so therefor they do not possess even close to the same magnitude of intelligence as humans do. If there is some scale of significant intelligence that should dictate what is acceptable to kill, animals violate it all the time, and so your entire argument falls apart. If anything, a cognitive function scale would be an argument FOR humans to kill ANY other animal, because clearly any other animal is not even in the same league as humans are with regard to intelligence. In fact, I'm not so sure you can even say that animals have ANY intelligence in the same manner that humans do: I've killed a pig and had other pigs come in and happily lap up the warm blood pulsing out of the dead pig's neck, without any clue that I was going to kill him next.... that is to say, pigs are ******* stupid. When any other animal besides a human invents a cell phone or a space ship, then I might consider them to have similar cognitive abilities. Until then, I want to eat dolphin bacon at some point in my life.
Lots of misinformation in the above. Some animals kill other animals for food, but for survival. They normally have no option. Those animals do not have the ability of being moral agents. Other animals do possess self-awareness and can be considered in the same "league" as humans. Lack of inventions doesn't mean the species is of significantly lower intelligence. Nearly every human creation can be attributed to one anatomical function: the hands. It's not fair to judge other animals for their lack of creations when they don't possess hands. The hands are also the reason for our superior intelligence, otherwise we wouldn't be much different from other animals. You are very wrong, pigs are not stupid. They are highly intelligent land animals. Using the dead pig's blood for food sounds more like they've been starved and provides no clue of their level of intelligence. Also note that the Hierarchy of Animal Value Scale does not argue that humans shouldn't eat any animals. It's more of a guide in determining which animals have different rights and to provide a moral compass for the level of treatment for various species.
Killing humans for food is only wrong because we are ourselves humans. If there were some stronger, smarter species that ate humans, could we say that were wrong?
Cannibalism is wrong because it's cannibalism. That's how your first statement reads. Yes a species superior to us that kills humans would be acting immorally.