In a philosophical sense this idea is based on a notion of life being morally ‘sacred’ regardless if it is a human or an animal life. In extension of this advocates argue that animals are entitled to freedom rights similar to those of humans, notably the right to their own life. To most people however, eating meat is the most natural thing in the world. There is a good reason for this intuition too. It is currently the dominating theory within natural sciences that consumption of processed animal protein has been a crucial element in the evolution of mankind. Studies show that it would have been biologically impossible for humans to evolve such a large brain as the human brain without meat, and to that end the conclusion is we owe humanity itself to the consumption of animal protein. Quite simply, humans are omnivores by evolutionary design. 

A comprehensive study has shown 84% of vegetarians eventually go back to eating meat, some 30% of those saying they experienced specific health-related symptoms while on a no-meat diet. While some people cope fine with a meat-free diet, others clearly do not, and on this backdrop it seems rather out of order to claim meat is murder. 

In addition to meat eating being somewhat embedded in the human DNA, there are a number of other problems associated with the idea of “meat is murder”. If life itself is universally sacred, are trees and plants also in the scope of moral concern then? Are insects? Where do we draw the line, and why do we draw it there? The next problem arises when considering all the wild animals which inevitably are dying in the fields while humans cultivate crops for plant-based diets, just as there are questions about important medicine which can only be developed through animal experimentation, or pest control which amongst many other benefits prevent the spreading of diseases. 

While meat is murder may be a captivating slogan, the universal freedom rights are exactly based on the idea that humans are capable of understanding the concept of freedom, hereunder the freedom to express your thoughts and ideas. Thus, meat may be murder to a tiny number of people in this world. To most people meatis simply a part of a healthy, balanced diet as well as a legacy from our human evolutionary history. What is not natural nor acceptable in regards of mankind evolution is the current and generalised food waste of such precious resources. Farmers are well aware and often the first to engage in the fight against food waste.    

Sources: 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5417583/  
– https://time.com/4252373/meat-eating-veganism-evolution/
https://www.berkeley.edu/news/media/releases/99legacy/6-14-1999a.html  
https://www.psychologytoday.com/intl/blog/diagnosis-diet/201903/the-brain-needs-animal-fat