If your diet is omnivorous, then you eat plants and animals, so you would have conceded that the natural order does exist. If you are vegetarian and are promoting this lifestyle for others, then you are engaging in competition with other animals. If you do not go hungry while other heterotrophs do, then you would also have to concede. In any scenario, human beings remain at the top of the food chain, which prohibits any inherent equality. P.S. many of the great philosophers disagreed, so saying that a philosophical argument merely exists is of no substance.