The debate about vegan ethics frequently devolves into attempts by those opposed to veganism to prove that there are situations in which it is morally acceptable to consume animal products. If they can prove that it is acceptable to be non-vegan in one situation, the thinking seems to be that they have proved that it is acceptable never to be a vegan. Thus, because it is not morally objectionable to eat the carcass of an animal who died of natural causes, we are told that it is acceptable to eat animals full stop. That is absurd, because it is equivalent to saying that we can steal, rape, or kill whenever we want to do so simply because we can engage in voluntary commerce, have consensual sex, and kill under some circumstances.
Neil H. Buchanan, Situational Ethics and Veganism, 97 B.U. L. Rev. Annex 1 (2017)