This is an interesting question because it's not easy to answer. It is assumed that prevention of pain is the biggest ethical concern
Vegetarianism goes far deeper than just prevention of pain:
- It is concerned with the right to a full life of every living being
- It realises that on average 20lbs of grains are required to produce 1lbs of meat
- To produce 1 lb of beef requires 12,000 gallons of water. Only 108lbs of water is required for 1lb of grain.
- The rate of species extinction (animals, insects, marine, plants) has exploded in the last century as a result of clearing of millions of acres of rain forests and jungles throughout the world as a result to animal rearing and the need to produce animal feed.
- Pollution from animal farms have negatively affected lands, rivers and seas globally resulting in increased phosphates, nitrates, decreased dissolved oxygen, increased temperature and increased turbidity
- A 2006 UN report assessed that meat and livestock industry contributes about 9% of total anthropogenic carbon dioxide emissions, including 37% of methane and 65% of nitrous oxide emissions.
- Livestock in New Zealand represents up to half of the country’s greenhouse gas emission
- The production of protein from grain-fed animals requires eight times as much fossil-fuel energy as the production of plant protein
Also meat is not healthy. Our bodies are not designed to eat meat. Anatomically we are herbivores. Although most humans are ‘omnivores’ in so far as they eat meat and plant foods, the anatomical and physiologic make-up of the human body points clearly towards a dominantly plant-based diet as the ideal for health.
The main causes of many major illnesses today are as a direct result of meat eating - many cancers, heart disease, diabeties, strokes.
and it is also assumed that being a carnivore is a bad in itself.
It can be considered bad for humans because of the many negative effects resulting from our consumption; On our health, on the planet, on so many uninvolved species, on the quality of life of the actual animal, on the many human affected because wanton waste of a few.