There is quite the difference between slaughtering an animal for food, and murder. Do you disagree?

Raising animals for meat is not energy inefficient. Those cows control the grasses and help with natural succession of trees and shrubs, while fertilizing the soil and providing nutrients for many animals. It costs literally nothing to leave a cow in a field, and it makes the field better.

What's energy inefficient is trying to grow a thousand cows in a feedlot.