(hopefully in the right thread this time
I think there are several distinct (but not independent) types of argument about the 'rightness' or otherwise of animal eating:
the practical (whether alternatives exist given the circumstances),
the health related,
Most of these arguments can be viewed as posing a moral question since they involve the environment and people's health.
Starting with the moral/ethical:
It seems to me the nub of the argument is about causing unnecessary suffering to animals. Obviously by breathing and walking down the street we kill millions of living organisms so it's not about the killing its about the suffering. Is the suffering we cause justified given our dietary needs and desire for certain tastes? In any case there seems to be a big difference between whether people think it is justified and whether they care if it is justified. This difference is illustrated when you feel sympathetic to the cause of the RSPCA and yet eat at McDonalds or buy Tecso 'value' meat or battery farm eggs. This moral myopia is maintained through mental conditioning ('farmers are all good, honest folk in touch with nature and who care well for their animals', 'meat comes from clean shrink wrapped packages on supermarket shelves', grilled steak is a natural food), habit and deliberate avoidance of the hypocrisy. ehem.. Of course it's easier to care about something you spend time with. Of course not all livestock live unhappy lives. There are farmers who really do care about animal welfare and look after their stock very well, don't send them on horrendous journeys to their slaughterhouse and kill them humanely. These animals probably have a much nicer life in the farm than they would in the wild. The objections to eating meat from these animals are part of the other types of arguments. Does anyone still believe that animals suffer no more than vegetables? *snicker*. Almost as funny is that some people think its better to live a doomed life of pain and suffering rather than never be born, well, if we didnt eat them, they wouldnt even be alive. What are you going to be sorry for if you never exist? Or, put another way, is it better to raise an animal that lives most of its life in misery, make damn sure it reproduces, kill it after it does and then raise the little animals in the same way to the same fate ad-infinitum, or, just stop the whole cycle by killing what artificially high population we engineered that cant be sustained and, if we must, eat the last of it? Which is better from a moral point of view?
The practical (whether alternatives exist given the circumstances):
Sure if I lived in the north pole or the barren grasslands of north America I'd eat meat too (until I moved somewhere nicer anyway). I have no problem from a moral standpoint with people who live in harmony with the environment, respect it and eat meat out of necessity. Fine. But 99% of the population arent in that position.
The fact as far as I can tell is it's a lot cheaper to produce grains, seeds and vegetables for human consumption than meat, simply because it's more energy efficient and there are less steps in the chain (generally). Producing meat as a very occasional addition to an otherwise vegetarian diet is a very different business to producing it on the mass scale it is for daily consumption. For mass production to be economically viable the animals need to grow fast, the food/weight ratio needs to be maximised which means steroids, unnatural diets and antibiotics to delay disease from the unnatural diets. You can't just let them roam around in fields eating whatever, they wont grow quick enough and space is a big expense. So the animals need to be packed in tightly. Even so the animals eat the kind of foods we eat (when they are fed on the grain and been rich diets in factory farms) and since their digestion is not 100% efficient and they use lots of energy for things other than growing, the whole process is much less efficient than just eating the beans and grains ourselves. Of course then there is the effluent disposal, the heating, the lighting, the water supply (and it's a LOT of water) and the transport (animals don't pack as tightly as beans, try as they might.). Basically eating animals as a main part of your diet is expensive. Eating animals that were well looked after and fed a natural diet is even more expensive because the throughput is lower and they require more land. I think at the very bottom end of the market (beef burgers, chicken nuggets, fish fingers, pet food) it is possible to approach the efficiency of a grain/vegetable based diet by totally disregarding animal welfare, environmental impact, health impact and sustainability. You just have to cut corners everywhere, feed the animals what are basically waste products with high calorific value and recycle all the bones and organs into God knows what, then you might say its almost efficient.
The animals we eat are mainly herbivores (omnivores in the case of some birds and fish). The more animals we eat, the more crops we must grow. The more crops, the more forestation we must destroy (much more than if we just grew the crops to eat directly since eating animals is far less efficient). The faster the animals have to grow (for meat to be economically viable) the faster the crops have to grow which means lots of fertilizers and pesticides and top soil erosion. Then there is the waste that lots of animals in a small space produce. It's fairly toxic and it gets flushes into rivers and streams causing death and disease to wildlife and people. Then there is the environmental impact of producing all the energy to fuel the whole inefficient meat production system. Also pumping animals full of antibiotics encourages diseases to mutate and become resistant. Apparently quite a few of these diseases also affect humans. oops! With fish the environmental damage caused by over fishing is to the food chain. Simply put, A eats B eats C eats D eats E. We fish too many C, B starves, so A starves. The population of D expands because C is eating it at a much lower rate, which putting stress on the population of E and also whatever creatures eat the same as D since there is now more competition for E. It just breaks the whole chain.
The health related:
Which diet will make you live longer, suffer from less diseases and feel better? Statistics and personal experience (about feeling better anyway) both say a vegetarian diet. This is actually less clear cut than the other arguments and people's metabolisms and enzyme production vary. But as far as I can tell from what I've read, for the vast majority of people it's a tie between a purely vegetarian diet and one that incorporates a small amount of animal protein. Large amounts of it appear to be bad, essentially because you have to cook it which denatures the protein making it less well digested, causing toxins in the body. besides the fibres (not dietary fibre) in meat make it more difficult to digest than most vegetable foods anyway. The longer food spends in your intestines the more it rots and festers But a little, every now and then isn't too bad apparently. Then there's the fact that it's much easier to get food poisoning from meat than vegetables. B12? If we ate organically grown veg, and perhaps a little dairy or eggs no problem. Also brewers yeast has plenty.
Obviously meat was a critical part of our diet when we were living in caves and huts, before we developed agriculture. It's winter, you're out of seeds and roots, what are you going to eat? An animal of course. Does that mean we should eat them now, because when we were cave or hut dwellers it was eat them or starve? Does it mean it's healthy to eat meat on a regular basis? I don't see why. Just because we evolved to be able to cope with certain foods doesnt mean they are good for us, or necessary, where alternatives exist. From an evolutionary point of view (but not necessarily a biological one) grains, beans and pulses arent a very natural food, and there is some evidence to suggest we are better off sticking to seeds, nuts, roots, vegetables and fruits. However since cooked grains, beans and pulses are loosely speaking nutritionally roughly halfway between meat and vegetables they seem to be a good compromise for calorie and protein dense food. You can live on rice and beans alone but most could not live of a 100% meat diet.
This seems to be the clincher for most people. Everything else is secondary, if it tastes nice then it gets the thumbs up, regardless. All the other arguments are rendered void in the face of a satisfied tongue. There is a certain texture and mouthy feel to meat. That protein and fat, (and all the herbs and salt added to improve the flavour) tastes good. Once it's on the supermarket shelf, it's very convenient to eat. Meat, two veg, seasoning. Simple. However... since it's the denatured protein (denaturing usually improves the taste), fat and seasoning that make most of the flavour, the effect can easily be recreated with a little knowledge using vegetarian substitutes. The convenience point sticks, but only because society goes to great pains to make eating meat convenient, not because it is naturally.
In conclusion, if you are concerned about reducing unnecessary animal suffering, economic burden to society, environmental damage and health risks to yourself its very difficult to recommend eating meat. The evolutionary argument for eating it seems mute and pretty tenuous. The practical justification is only valid for a minute fraction of people. So of course the main reason people do it is because they just like the taste and cant be bothered to change their habits. What was it Forest Gump said?