The fact is that, humans consider anything not human as fair game. Technically, eating meet is not necessary for survival, as we can get most of the nutrients in it from plants. In addition, due to the nature of food chain, plants contain more energy than animals as their energy source is from the sun. Aflnimals then eat these plants, and in any conversion of energy there is always a decrease in the amount of useful energy converted. This energy might have gone through different conversions as canivores feed in herbivores and other canivores feed in carnivores over time, that when it eventually gets to man, the energy present in the meat will be drastically lower than the one originally in plant.

If this is the case, this means that man is killing animals for meat solely because he can, we it has been explained plants contain far more benefits than animals, nutrition wise.

So if it is the case that man rears animals just because he likes the taste, at the detriment to that animal's life and the ecosystem at large, I believe it is unethical.