For starters, the "needless" context is satisfied with this statement from the Academy of Nutrition and Dietetics: "appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle"
If it's not wrong to needlessly kill animals, is it wrong to needlessly kill humans? If yes, this implies there is a difference/some differences between animals and humans that allowed you to make this distinction. What are these traits? If you applied these traits back onto a human context, would it be okay to needlessly kill the human?
Please consider going vegan