The Desert Island argument is a ubiquitous late-game strategy for those who have exhausted or nearly exhausted their case against veganism and it generally goes like this, “Okay, vegan. I get that eating animals is bad for the environment, bad for people's health, and bad for the animals, but are you telling me that if you were stranded on a desert island and you had nothing to eat but pigs-in-a-blanket and wild grouse, you would rather starve?” The intention of this argument is to call into question the strength of the vegan's moral convictions by suggesting that if she were given the choice between starvation and eating animals or animal by-products, she would abandon her vegan convictions and eat whatever or whomever she could get her protein-deprived hands on.
What underpins this argument is the ludicrous assumption that any ideal for which someone else is unwilling to die is somehow not worth taking seriously. And never mind that many vegans would rather die than take the life of another animal. What this argument also fails to acknowledge is the difference between killing as matter of pure necessity and killing as matter of convenience or pleasure, which are by no means morally equivalent. Killing as matter of survival (as only a small handful of subsistence hunters do) is a vastly different thing from killing for the sake of sensory pleasure or out of convenience.
A much more pertinent question (and one, incidentally, for which we can take no credit) is the following: Let's say that you, eater of meat, eggs, and dairy, were given a choice between two life-style alternatives. On the one hand, you could get all the nutrients and calories you need from a healthy, cruelty-free, vegan diet consisting of fruits, vegetables, and grains, all of which are readily available at almost any supermarket. On the other hand, you could subsist on a diet that necessitates cruelty, exploitation, and slaughter and which contributes significantly to climate change, deforestation, water scarcity, water pollution, ocean “dead zones”, habitat loss, species extinction, and world hunger.
Given these alternatives, which would you choose? Answer the latter question honestly and then try to ask the former with a straight face.
Your argument is invalid.