Out in the wild, there are many animals who live by your rule (that is, no eating meat). You know what they're called?
Prey.
When a mountain lion comes along and decides you look pretty darn tasty, there's only one way out. We humans are really slow runners--you're not gonna escape that way. Your only chance is to kill the mountain lion. The only reason you get away with vegetarianism as your lifestyle is because a bunch of other people are driving away or killing the mountain lions who would turn you into a weenie roast.
The barbarism you spoke of is pretty much just a fact of life.
Human beings are different, we are more empathetic than any other creature and, more than that, we can consciously acknowledge are own empathy, thus creating a moral compulsion to act upon it. This, arguably, requires humans to show a compassion to animals that a natural predator is unable to. While a lion or wolf is compelled by natural instinct to kill, humans are compelled by our empathy to care for other living creatures. This does not exclude us from the killing of animals for food, but, in this day and age, where it is possible to live a healthy vegetarian lifestyle, perhaps we are compelled to do so. I'm not saying that we should- I'm honestly not shore myself- just that making an appeal to "natural law" does not work when you factor humanity's, shall we say, "higher state of mind" into the equation. I'm sure Ecofarm would agree that a human can morally kill and consume an animal, just that, perhaps, this is not so in our modern society.
As for the mountain lion thing, well, that's
really not the point. Defending yourself against a predator is justifiable, while Ecofarm's argument is that the killing of animal's for meat is that it is
unnecessary, and therefore unjustified. Trying to defend your hamburger because "mountain lions could eat you" is pretty much, well, I'll be frank, completely and utterly absurd.
That's what always puzzles me about people attributing our sins to "human nature". Surely, human nature is to be empathetic, to be, for want of a better word, "good"? It's the animal in us that drives to selfishness and sin... Pedantic, perhaps, but I think it reflects some underlying philosophical idea, although I'm really not sure what it is.