For the most part, animals are parasitic on plants- we eat them in order to retrieve their nutrients and give them nothing in return. Goodbye Earth-loving vegans, you are now officially a parasite. Almost all food chains can be derived from some sort of plant matter. Take the sabor-tooth tiger who eats the mammoth, who then casually destroys millions of small helpless plants. Super selfish.
As one famous biologist put it biology is the study of plants and their parasites. And it appears that vegans are the epitome of just this.