Whether you believe the Bible or not, it states that God created all animals to be herbivorous (vegetarian). 29And God said, "Behold, I have given you every plant yielding seed that is on the face of all the earth, and every tree with seed in its fruit. You shall have them for food. 30And to every beast of the earth and to every bird of the heavens and to everything that creeps on the earth, everything that has the breath of life, I have given every green plant for food." And it was so.
So since the average carnivore proves that to be hogwash, why would you quote it as an example. The only thing it shows is how out of touch with reality the bable really is. Did all the herbivores evolve into carnivores since it was written?
Whether you think it was written 3K, 4K, 6K, whatever years ago, the Bible (which you may believe or not) said that God created man to be a vegetarian. As for Cain? I've never heard he was the first to eat meat, but I have read scholars who believed original sin led to man's eating meat. The fact that their clothing was made from animal skins was a reminder of their sin.
The point is: No one can say that God, as described in the Bible, created carnivores. He created man who became a carnivore just as he became a sinner.