But Lions Eat Antelopes!
A common retort meat-eaters give to ethical vegetarians is that since animals eat each other, humans should be allowed to eat animals.
In no other moral question besides meat-eating do humans look to other species to guide behavior. (And carnivorous species at that; people could just as easily turn to herbivorous animals for ethical guidance).
The same could be said about turning to other human cultures, such as Eskimos. People in our society never look to the Eskimos (Inuit) for guidance in ethical matters other than when it comes to eating animals. Instead of turning to Eskimos, we could just as easily turn to the Jains (who do not kill animals).
Even if humans should model their behavior towards other species based on the worst treatment that one non-human species gives to another, humans still go beyond such treatment: No other species of animal factory-farms members from another species, causing them months or years of misery; or systematically slaughters them.
For the most honest ethical answers, people do not to look to others' behavior for justification. Rather, they consider the potential beings impacted and then weigh the good and the harm.
Why should the question of eating animals be any different?
It would be nice if there were some species more intelligent and more powerful than humans, but also more benevolent. They could stand as an example of why we would not want the ethical principle of the universe to be "Feel free to treat other species according to the worst treatment you can find among any other two species."
