In an interesting but brief exploration
of the ethos of veganism, its corrolary, animal "rights, and the overall incongruities of the philosophies in the context of species dominance, a guy by the name of Rhys Southan considers the effect of a landing on our planet by a race of vegan aliens. If they are philosophically anything like us, he suggests, we're in deep trouble.
If our intergalactic superiors landed here, but had no interest in eating us or our fellow animals, the first thing they could do is rob our stores, homes, farms, and warehouses of all our fruits, vegetables, beans, grains, and vegan convenience products. Without violating any vegan principles there would be no limit to the amount of food vegan aliens could steal from us — vegan ethics allows for humans using all the plant matter they want in the world, no matter how many animals starve as a consequence. Aliens could cause the worst famine humanity has ever seen, but it would be entirely compatible with vegan ethics.
Depending on how much land was required for the vegan alien cities to accommodate all their alien vegan restaurants, alien anarchist bookstores and alien warehouse lofts, the vegan aliens might or might not set aside some land for humans to live on. Because our habitat would be fragmented to suit aliens’ desires regardless, it would be difficult or impossible for us to redevelop agriculture of our own, or gather enough food to survive. Any habitat they left for us would never truly be ours anyway, because if the aliens ever wanted to increase their population or just spread out, veganism doesn’t stop them from taking more land.
All in all, regardless of how "green&sustainable" going vegan seems, and despite its ego-stroke advantages, in real terms, it's no more effective than choosing to drive a Prius; the only real benefit accrues in the smug-factor that the choice affords the driver's sense of self-esteem and moral superiority. Environmentally speaking, when total costs are tallied, it's more "green&sustainable" to purchase and drive two Hummers than one Prius, and vegans exert much the same effect, biologically speaking, in their decisions.
It's not their fault; it goes with the territory when one is the dominant species on a planet of finite resources but an abundance of life-forms. Something - and probably a whole lot of somethings - will lose out, regardless of how seemingly benign the intent of the dominant species (assuming intent in the first place). Indeed, as has been noted here on occasion during previous discussions, there exists but one way to assure limited impact, yet, curiously enough, not one of the Save The Planet™ types, from AlGore to the most rabid PeTA and ALF supporters, appear willing to take that step.