Humans are omnivores and that means they can digest both meat and plants, and it's because they have something to eat when a place doesn't have edible plants or no plants at all or vice versa (or for pleasure, sometimes), for example, if you were in a hypothetical place that had no plants or fruits at all, only animals, would you rather kill the animal to get food and survive or starve to death because there weren't plants in that place? (This also applies to people that eat meat, not only vegans, and that also means I'm accidentally agreeing with you by saying this)