This is excellent example of the fallacy of argumentum ad naturam.
http://www.fallacyfiles.org/adnature.html "Male lions commit infanticide of offspring sired by other lions. Other animals do it. Humans are part of nature. There's nothing immoral about humans killing other people's children."
The effects that modern humans have on other species, the environment generally and climate as a result of eating other animals does not even vaguely resemble the effects that animals who are biologically adapted to eat other animals have on other species, the environment and climate.