What about how other animals kill and eat each other?
There is a big distinction between the situation when a lion eats meat, and the situation when a human eats meat.  Lions can not decide to live on grain and vegetables.  A lion must eat meat or die. A vegetarian diet for humans, on the other hand, is actually healthier than one which includes meat.  Whereas lions must eat meat to survive, humans eat meat simply for the pleasure of tasting meat. 

There is another significant difference between lions and humans.  Lions do not raise their prey on factory farms, where animals are forced to endure a lifetime of suffering and confinement.