This is a very common argument used against vegans, the basic idea behind it is that since animals also eat each other, us eating them cannot be seen to be immoral, because we are just doing what all other creatures do. This is often followed with rhetorical questions about whether vegans would force a lion to go vegan too, or why we aren’t protesting lions and wolves. Some people even have the bizarre idea that the ultimate goal of veganism is to stop animals eating meat too, since we view all animal death as inherently bad.
This argument stems from a basic understanding of what vegans actually believe. The assumption is that vegans are against any animal being killed for any reason, and that we view any animal dying as an intrinsic evil. Though this assumption is understandable, it is completely inaccurate. Vegans oppose animal exploitation and the unnecessary slaughter of animals for human benefit. The issue for us is that exploiting and killing animals is placing our desires, taste preferences and convenience over their right to be alive, and placing the interests of humans as inherently more important than those of any other animal, even when their needs are clearly greater than ours.
Necessity is the key concept here. The vast majority of humans can be perfectly healthy while avoiding killing animals, doing so is therefore a choice, and like any choice, it is open to moral criticism. For wild animals however, eating other animals is a matter of survival, they do not have the option or the capacity to make a moral choice to avoid harming other creatures. There can be no moral judgement about an act if the being performing it could not have chosen otherwise, and this counts for humans too. It should be self-evident that a lion hunting gazelle because they and their cubs will starve if they do not, and a human buying pre-packed meat from a supermarket containing hundreds of other options is in no way comparable. An obligate carnivore hunts for survival and because they cannot exist in any other way, and therefore places their survival above that of other animals, not their taste preferences.
The point that we cannot compare obligate carnivores and omnivores with modern humans is an important one, because it is something that we as a species vehemently believe in every other context. We justify our exploitation and consumption of animals on the grounds that we are higher than they are, and we deem any comparison between us and them as anthropomorphism. Moreover, we routinely deny that they experience pain or emotions the same way that we do, or that they are capable of thought in the way that we are. How then, can we justify eating animals on the basis that they eat other animals too? It seems to me that we compare ourselves to other animals only when it is convenient for us to do so, and the rest of the time we enforce a strict moral and intellectual distance between us, and baulk at the mere suggestion that humans and animals should be treated equally on the grounds that they are not like us. Either we are better than animals and we use that to justify the cruelty we inflict upon them, or we are the same as them and thus cannot be expected to behave better, but we cannot be both.
This is all part of the completely contradictory way we view animals. We are so utterly opposed to the notion of similarities between humans and animals that any comparison is deemed sentimental and unscientific, and despite decades of research on the topic, a good portion of us still will not accept that animals experience emotions in the same way that we do. We think of farmed animals especially as mindless, unfeeling automatons whose preferences do not need to be taken seriously, yet at the same time we use arguments like this one which rely on the assumption that these same animals are capable of moral agency, of weighing up decisions against one another and choosing which is the most ethical option. We think of ourselves as so much better than animals, yet we use their behaviour as our moral baseline and to justify our own actions. We make these comparisons very selectively too, taking our behavioural cues from obligate carnivores like lions, while ignoring the fact that many of our closest animal relatives are primarily herbivorous. We are also highly selective of which behaviours to emulate and which ones to ignore; animals routinely commit incest, killing for territory and infanticide, yet no one ever uses this behaviour in animals to justify it for humans.
Few humans seriously entertain the notion that we should imitate the behaviour of lions in any other context besides eating meat, and even fewer genuinely made a moral decision to start eating animals on the basis that carnivores in the wild do it too. We eat animals because they taste good, because we were raised that way and because it is convenient, not because we saw a pack of hyenas bring down a wildebeest and decided that this looked like the most ethical way for us to live. What is natural has no moral relevance whatsoever, and the fact that a specific behaviour is exhibited by other animals is certainly no indication that it is something that we should be doing ourselves.
Comparing obligate carnivores hunting with nothing more than their wits and their claws with modern humans living in an industrialised, consumer-driven society is so far-fetched that it almost sounds like satire. Justifying the consumption of animals on the basis that other animals eat meat too is nothing more than a convenient excuse, and the notion that behaviour is justified so long as it is performed by other animals is an argument which would not be taken seriously in any other context.