We evolved as omnivores, requiring meat as well as plant matter to survive, regardless of if t is humane or not. Therefore, "wrong" is a relative thing. — Life101
We evolved to do all sorts of things, but it does not follow from this that we
should do them. Indeed, we evolved to be able to consciously evaluate our actions and thus ascribe a moral value to them so it's entirely reasonable to
claim that killing animals for food is wrong. However, what makes an action morally 'wrong' or 'right' is the consistency of the arguments put forward for not doing so in accordance with the presuppositions on which these arguments are based. What makes an action
ethical is the strength of the arguments
and the presuppositions. Vegan arguments proceed logically from their presuppositions, and thus are internally consistent. However, vegan presuppositions are extremely flimsy.
Whilst is certainly true that, with care, a human can survive on an exclusively plant based diet, it does not follow that we
should follow a plant based diet. Animal flesh may not be 'necessary' for survival, but since survival is not the sole goal of most humans, vegans must provide other arguments for not killing and eating animals. Indeed, humans can also survive exclusively on animal produce, so we could argue that plant based foods are not 'necessary' either.
So why not animal flesh? Vegans claim that meat eating causes suffering. This is an intuitive claim based on an analogy between humans and animals. Since we generally accept that it is wrong to cause suffering to other humans, it appears to follow, by analogy, that if animals can suffer, it must be wrong to cause suffering to them also. There are all sorts of problems with this; qualitative and quantitative aspects of suffering for example. We know that humans suffer differently between individuals, so how can we even begin to quantify animal suffering? At best, all we can say is that animals experience something analogous to human suffering. We cannot begin to ascribe it quantities and qualities. Nevertheless, let's concede this to the vegans:
It is wrong to cause suffering.
However, it is conceivable that suffering could be eliminated from the supply chain. If I were to die instantly in the next few minutes, it's hard to see how I would suffer. Likewise, a quick and painless death for an animal is not in itself 'suffering'. Going even further, a mutation could conceivably result in an animal that 'wants' to be eaten so not only would it not suffer, it would actually benefit from being eaten.
If we can remove suffering from the equation, what other reasons are there to not consume animals? The environmental argument proposes that animal production is inefficient since it involves a seemingly disproportionate ratio of biomass vs nutrition. Whilst this is true, it is only 'wrong' if we accept the unstated premise that 'we should always minimise biomass'. Animals' consumption of plant biomass is an inevitable part of the trophic web. If it we could fine tune it so that it was not environmentally damaging, this objection to meat consumption dissolves. Indeed, meat consumption may even be an environmental boon; take the European peasant's pig which consumed organic waste including human faeces and was then killed for food. Surely, this pig is the opposite of environmentally damaging and should be encouraged? An animal like this could thrive in a vegan household since vegans defecate up to twenty times more than normal people and this huge amount of vegan faeces places a great deal of strain on sewage services and scarce water supplies.
Vegans are also frustratingly inconsistent in their approach to plant suffering. It does not follow that since it is seemingly impossible to empathise with plant life due to its difference to us that it is therefore acceptable to eat it. Humans do not provide the benchmark of suffering by which all other life forms may be measured. It may be that plant suffering is greater than animal suffering precisely because they don't possess animal sensory apparatus; who knows? But in order to be consistent regarding their desire to prevent suffering, vegans should accept their ignorance, err on the side of caution and avoid eating plants altogether. Of course, they do not do this, instead they make hasty presuppositions of convenience that allow them to do continue to do what they want
and to retain their purported moral superiority.
My problem with vegans is not what they eat; I don't care, but I don't think they should care what I eat either since they are incapable of convincing anyone but themselves that the underlying assumptions of their morality stand up to ethical scrutiny.