Being human now, we have the ability to discriminate right from wrong and to make choices. We are well aware of the faults related to eating meat and can also afford not to eat meat. Yet we do not or are unwilling to make the right choice. If and when we do take rebirth as animals, we will : 1) want to eat meat and meat alone, regardless of how delicious fruit and vegetables may taste; 2) not know the faults of eating meat; 3) not have the ability to choose. There will be no way we can avoid being carnivores by then. If we choose to be meat eaters when we  can be otherwise, being carnivores in the animal realm would just be a natural outcome. 

~Depicted from FROM BELIEVERS TO BODHISATTVAS