Animals are less intelligent than humans and therefore can be slaughtered for food. Arguments also include more specific indicators of intelligence, such as the ability to speak English or anticipate suffering.
We don't consider that a more intelligent adult should be issued hunting licenses for less intelligent adults. We also don't regard the mentally disabled or children with any less regard than that of an intelligent adult - in fact, we usually do exactly the opposite, our natural instinct is to defend the defenseless in any other context.
Consider this scenario: we travel to another planet and meet a bunch of beings not unlike ourselves. They are better than us at calculus, but worse at emotional intelligence, so they couldn't cooperate to build a spaceship (that meant we visited them first, rather than vice-versa). Who gets to eat whom? Or is emotional intelligence not "real intelligence"... as declared by whom?
In the case of more specific indicators like language, whose language? If aliens use pheromones and body language to communicate (like animals do), then does that mean that they would get to eat us on the basis that we can't smell their pheromones or understand their movements? Or do we get to eat them on the basis that they perhaps have difficulty with some aspect of English grammar?
If we, for instance, just draw a line at doing math, then we shouldn't eat animals. Also, as a society, we frown on the eating of golden retrievers, which are no more able to do math than other species that we don't offer any protection towards. So even on a species-by-species basis (which itself is untenable) what's the real metric? If we base it on specifically symbolic math, should we be able to eat cavemen?
If we don't like math, and instead we pick any other particular characteristic, or some sort of sum total, that also doesn't hold up: pigs are also generally regarded as smarter than cats, and we don't eat cats. Also, are we allowed to kill and eat stroke patients or the mentally handicapped who didn't do any of that or who have lost that capacity? So in all cases, we don't actually use intelligence, either in any specific category or in any general form, to determine what we can and can't kill.
The most obvious conclusion when one witnesses an animal suffering is that intelligence has nothing to do with it. When we see an animal caught in a fence or somehow otherwise suffering we recognize that it's not about some intellectual capacity towards something like abstract reasoning. So it's already special pleading to base morality on anything other than capacity for well-being and suffering.
But then it's even more arbitrary to say it's based on intelligence - that is - on an arbitrarily chosen specific version of intelligence, and then one can sort of (again) arbitrarily pick and choose which animals we selectively apply the intelligence towards based on how good they taste.
By eating meat we're hurting other people in addition to animals, so this argument doesn't address that issue, which doesn't satisfy this argument's own criteria.
And therefore all the same problems apply.