As a vegan who practices the lifestyle (primarily) because of ethical reasons, I get into some pretty funny (sad) conversations. Two challenges I am often presented with is that 1) humans are justified in eating animals because we are at the top of the food chain, and that 2) animals eat other animals in nature so why can't we? Simple, eh? Case closed? Well, not so much. These are challenges which many vegans find intimidating, but they aren't really adequate challenges at all, for a number of reasons. I'll look at a couple here.
The first, and a less obvious one, is that technically speaking human beings are not at the top of the food chain at all. Scientifically speaking [and most people today seem to love appealing to the "authority" of Science], to be at the top of the food chain, or to be an apex predator, one needs to only eat other animals (here-do-humans-really-rank-on-the-food-chain-180948053/?no-ist">e.g., tigers, boa constrictors, crocodiles). Humans actually, are more herbivore than carnivore, and in an actual scientific food chain, we actually rank alongside pigs and anchovies lol. Again, true apex predators are those such as polar bears and orcas, not omnivorous human beings. But one could say 'Oh, sorry, I don't mean scientifically then, I mean that there are no other animals which hunt and eat other animals as human beings do, therefore, this is how we reach the pinnacle of food chainness.' Well, thanks for the qualification, but that's not completely true either, as there are many animals which will feed on (and hunt) humans. Just watch some 'safari gone wrong' videos for support. Embarrassingly though, there are much smaller animals which not only feed on us, but which can outright overwhelm us and kill us easily enough if afforded the opportunity. One such example is the microscopic ameoba Entamoeba histolytica (for all you hardcore science geeks, check out the academic paper -->here<--), which infects 50 million people and annually kills about 100,000 of them. This little guy kills human cells. This means that this teeny tiny little life form is capable of killing large numbers of human hosts. Suddenly our self-perceived dominance of the game we played as kids ('King of the Hill') is not so sure.
The real facts bear witness that humans are not at the top of some self-conceived food chain that we ourselves dominate because we have imagined it as such, but that we exist in what is referred to as a food web, wherein all forms of life are interconnected and thus subject to a variety of codependencies which are necessary for the possibility of life on earth as we know it. Therefore, Another, possibly more important argument need be made though, and this is drawn from the philosophical idea that we are a species with moral agency. Aside from marginal cases, humans are generally recognized as moral agents, and other animals as moral patients. This means that human beings have developed a cognitive ability which makes us accountable to such moral ideas as rightness and wrongness. We are capable of acting according to these notions and are held accountable for them as no other animal is. This presents us with an interesting philosophical problem as moral agents when confronted with adhering to (or not) such natural law as a hierarchal "food chain". So, as human beings, on top of this illusory "food chain", we must ask ourselves what characteristic we possess which maintains our position on top? Superficially, many would say that it is our strength, but this is surely untrue, as many animals are much, much stronger than we are (e.g., rhinos, hippos). It is far more correct to opine that it is rationality, or intelligence, which places us atop other species of animals. After all, even though we would be at a severe disadvantage with a rhinoceros one on one or mano a mano, using our rationality we could surely devise a way to come out on top. Therefore, it is more plausibly argued that it is rationality, not strength, which affords humans a place of prominence over other animals. But it is this same rationality which actually disqualifies us from using the top of the food chain argument at all! As moral agents (beings with superior rationality), we are not subject to blind obedience to natural law, or predation, as practiced instinctively by moral patients. It is precisely our rationality which demands we make moral choices about our dealings with other animals. If we conclude that our dealings with other animals in various instances are immoral (or unjust), then we do not simply follow the law of the jungle, but we assess that injustice and are capable of choosing differently, ethically, in light of our conclusions. To say that humans can eat other animals simply because we are at the top of a "food chain", and because other animals eat other animals in nature, belittles the moral responsibility of our species and betrays the very thing which we claim is different between our species and other species! The argument just does not, nor can not, hold. Now if one were to dwell on our food choices and conclude that humans are justified in eating animals then I guess the discussion would continue in different ways. But this conclusion would not be based on the fallacy of the top of the food chain argument, and would require different premises. Given that the vast majority of us eat animals that are intensively raised in factory farming operations, I am not sure what reasons one could give as justification, but the fact that the majority of us still demand the existence of such "agriculture" argues the case for it. That however is a different discussion from what I am talking about today and demands separate consideration. However, to me at least, it appears that eating animals solely on the two assumptions I usually hear, that 1) our own (biased much, perhaps?) species is at the top of some non-existent "food chain" (as opposed to a more correct food web), or that 2) in nature, animals eat other animals (so why can't we?), are based on fallacies which betray the very thing which we distinguish ourselves from other animals, our rationality. Maybe it's time we use this rationality (or higher intelligence) for better things than self-exaltation.