This is a much debated topic these days. The supporters of veganism and the meat eaters have their own arguments and views on this matter. What is really good or bad depends on lots of factors. Let us discuss both the things.
We see in the nature that herbivorous animals eat plants and leaves of trees. Carnivorous animals feed on herbivorous animals. When they die, scavengers come and eat the body of the dead animals. Bacteria, fungus and other microscopic life forms do the last thing. They separate the compounds of carbon, oxygen, hydrogen, nitrogen etc. from the decaying bodies and send back them to the nature from where plants absorb them and the life cycle goes on.
Man is naturally an omnivorous animal. Our primitive forefather could digest plants. When they started to eat meat, they become more intelligent as it was easy to digest in comparison to the cellulose of the plant. So, we have long intestine as herbivorous animals have and also we have appendix a sign of our vegetarian ancestors. However, we have molar teethes like other carnivorous animals and our eyes are positioned on our face in the same manner as the eyes of other carnivorous animals are placed. Therefore, it can be said that we humans are omnivorous creatures.
The living world receives energy from the sunrays when the plants absorb it and make molecules of glucose from it. Herbivorous animals eat plants and from them, energy transfer to the top predators. But in each step the amount of energy decreases. It takes a herbivorous animal to eat plenty of plants to grow and it also takes a carnivores animal to eat many animal to get the same amount of energy which the plants received. Therefore, we need to deploy lots of resources to raise animals. It is easy to grow wheat then to raise a pig or buffalo. So, the animal rearing for meat, puts a heavy burden on the resources of this planet. Our population and energy requirement is destroying the environment of the earth and the meat industry is making matter worse. Meat industry causes a lot of pollution. Also, the meat industry causes animals to suffer a lot. People don’t care about the condition of the animals while they are raised and transported for slaughter houses. Animals are living creatures like us and they also have senses and feeling like us. So, meat eating is definitely a cruelty against the animals and it’s unethical.
Propagators of veganism also say that vegan diet is healthier. It is free from fats and other harmful ingredients which are found in meat. Meat does not remain hygienic as bacteria grow fast in meat and it may also contain feces, blood and other body parts of the animals.
They further argue that meat eating increases problem of obesity and cholesterol. Red meat is associated with some types of cancers. So, the vegan diet is the healthy diet which is free of cruelty against animals and also eco-friendly.
On the other hand supporters of non-vegan food argue that man can naturally eat meat. Meat was the thing which made our mind sharp and helped us to be the top species. They say that certain vitamins like vitamin B group, D and K2 are not easily available in vegetable food but they are abundantly found in meat. Plants also have life, so should we not eat them?
They also argue that if plant eating animals are not killed, they will grow very fast and eat away all the plants and eventually die of hunger. Ultimately, the life from this planet will end. Also, man raises many species of animals for meat which keeps the genetic code of these animals to survive. Without meat eating, species of these animals will extinct as there would be no purpose of their life. Animal rearing also provides a lot of jobs. If it is banned, people will become jobless and this will have very bad effect on the social, economical and political stability of the world.
I think arguments of both the parties are rational. As Lord Buddha had proposed middle path is the best way. We should not become extremists on this issue. Excessive meat eating has a bad effect on this planet which we should reckon. But vegan food is also not sufficient for us. So, our diet must be balanced.
I will answer the question of 'why anyone would switch to a plant-based diet (ie become vegan)' from my perspective. It is a perspective of 'health' being 'holistic' and covering mental, as well as physical health. I will not argue the point about whether humans are naturally carnivorous or not, because, for me, this is a question of personal choice. There are healthy vegans, and healthy carnivores. I think the issue is deeper than biological/evolutionary predisposition. I see 'health' as unity and wholeness - body and mind. A state of unhealth therefore, is one of division and violence (the body or mind, divided, agitated - 'ill').
From this holistic point of view, everything is interconnected and what we eat has a deep, if largely invisible effect on our overall health and well-being. I see each individual as having the potential to take charge of their own health, primarily through diet.
Having stated the above, I will list the reasons why I am vegan below. The case is very suitably made by the following three documentaries, although there are plenty more sources of researched information.
Why I follow a plant-based diet:
We can choose easily.
Eat to heal and live
Live to eat...
A complex personal choice that involve daily habit and effort to acquire knowledge of food.