meat is murder
You're not going to have a good argument for this stance. That's a statement of ethics, perhaps approaching religious intensity, and thus not really amenable to logic and reason.
humans can get all their vitamins and essential nutrients from plants/soy/beans/vitamins
No, they can't. There is no NATURAL source of B
12 outside of animals of some sort. In cultures such as Jains that
appear to do so it has been found that they get their B
12 from, basically, insect and rodent feces contamination of their food. When such groups have moved somewhere such as the UK, where food purity standards are higher than in rural India, they invariably run into deficiencies unless they use supplements.
There was some research published on this back in either the '90's or 00's, can't remember exactly. Maybe it was the
Lancet? Anyhow, I no longer have easy access to such journals but you might, and being able to cite actual, peer-reviewed or at least vetted research would probably tickle your fancy.
We didn't evolve to eat meat, we're not really omnivore
Yes, we really are omnivores.
First, our closest animal relatives, the chimpanzees and bonobos, both are not only opportunistic meat eaters but chimps will also organize actual hunting parties. Female chimps will trade sex for meat (since bonobos pretty much exchange anything for sex, or simply fuck for any or no reason, impossible to say if such exchanges occur among them).
Second, top of that, while we are not carnivores in the sense of cats, our bodies unquestionably have the ability to process nutrients from animal flesh.
Third, the fact that we REQUIRE a nutrient – B
12 – that in nature is ONLY found in animal flesh is pretty strong evidence that we're omnivores and yes, we really DID evolve to eat meat on at least an occasional basis.
Animals that are true herbivores, such as ruminants, equines, and lagomorphs (rabbits and their kin) produce B
12 in their guts and either absorb it there (ruminants) or eat some of their own feces (rabbits) to get the needed amounts. Humans don't do that – we neither produce B
12 in our guts no do we (outside the mentally ill) eat our own shit.
As soon as vat-grown meat, or insect meat becomes available/affordable, i'll transition to that.
Insect “meat” is available in some areas, but in my country it's surprisingly expensive – edible mealworms, for example, cost as much as prime beef per unit of weight. Cicadas are freely available when in season.... said seasons being 17 years apart, which makes it difficult to make them a regular part of the diet (species with such long breeding intervals may have evolved such a mechanism to prevent predators from specializing in them).
Have you seen how badly animals are treated in factory farms
Well, it IS possible to avoid that. For example, for nearly a year now we've been eating eggs from what I call “happy chickens”. They're kept for their eggs, but get outside for free-range grazing every day (although on some of the really cold days this winter they apparently looked at the human in the doorway with a “are you fucking crazy?” expression and refused to go out, when pushed outside immediately ran back inside – not as dumb as their reputation would have them), are not subjected to artificial sunlight so during the winter their laying scales back, and otherwise live pretty amazing wonderful chicken lives. The eggs aren't fertile so you aren't killing any baby chicks. So it is entirely possible to eat non-factory farm animal protein.
Likewise I have neighbors that keep goats as pets but will take advantage of milk, and so on and so forth. Small-scale animal husbandry can be both kind to the animals and provide some animal protein to the humans.
Then there is the matter of wild food – there are an abundance of game animals. Granted, there is some bother to obeying hunting laws, observing licensing and season requirements, and so forth, and hunting is not as
reliable at the grocery stores or butcher shop but it's yet another option where the animal is not subject to abuse during life. Granted, those last few minutes might be pretty horrible but no worse than natural predators, and may well be quicker (predators don't hunt to kill, they hunt to
eat, and may start eating prior to death or unconsciousness in their prey).
Same for fish.
For that matter, you could either gather or raise your own insects/arthropods for eating purposes. Same principal as chickens, and people do it anyway to supply pet stores with food for carnivorous pets. Or, in one case, I knew someone who had a rat colony they started specifically for feeding their snake collection. Baby rats for the little snakes, grown up rats for the larger ones, and the rats also took care of all their kitchen scraps... it's sort of like gardening, but with more cleaning up of poop.
what it does to the environment
Farming vegetables, fruits, grains, and nuts can also be quite harmful to environment.
It's not what is being raised, it's HOW.
The Alaska salmon is an example of a fishery that is maintained at sustainable levels. Of course, the fishery rules being enforced by an arm of the US military (the Coast Guard) also has a lot to do with compliance. Alaska salmon isn't particularly cheap, but why should it be? (Certain sub-categories, like Copper River salmon which is highly seasonal runs even higher – about $90-100 USD per kilo this year).
Arguably, given the plague upon the land that white-tail deer have become in North America, I'd argue we should be eating
more of them so fewer would starve to death or get hit by vehicles. Cull the herds a bit more and those that remain will be healthier and live better. Yes, it's harsh, but it's absolutely natural for their numbers to be pruned by predation.
So – more use of wild protein (in a sustainable manner), and more use of smaller meat animals (chickens and rabbits convert plants to flesh more efficiently than do cows) would result in a smaller environmental foodprint, might even
improve the situation in some cases (too many deer areas), and provide animal flesh to humans in quantities sufficient for health.
why should I eat the flesh of another living creature
You don't have to.
First, I recommend killing your animal food prior to eating it. While some people DO eat live food it's very, very much optional and even a lot of omnivores are squicked out by it.
You DO require a small amount of animal-source food, though. You can achieve this via things like eggs or diary products.
From almost any angle, the arguments in favor of eating meat (unless you drastically cut back and consume only certified humanely-raised products that cost about ten times what you're used to) don't overcome the horror that is the modern mass-production of meat, eggs or dairy.
Since it (very roughly) takes about 10 units of plants to produce 1 unit of animal flesh, in a sense meat SHOULD cost ten times as much.
Also – there's a limit to how horrific dairy ranching can be. Unhappy cows don't produce much milk, so dairy
cows usually aren't treated as badly as beef cattle (the unneeded dairy bulls, though, usually wind up as veal. Veal calves live in a special circle of hell prior to the end of their brief, fucked-up lives).
At least these days options to factory-farm products are becoming more common.
There simply is no good logical or ethical argument in favor of eating meat if you're not a hunter gatherer, subsistence farmer or other highly impoverished person who legitimately needs the protein and lacks access to varied nutrition from other sources.
I think that's a bit restrictive. What's wrong with being a first-world hunter, provided one observes the law and hunting ethics (try to achieve a quick kill, do not abandon a wounded animal but track it, etc.)? Particularly since such hunters keep down the numbers of some species (deer) that would otherwise be even more of a pest species than they currently are? The alternative for deer would be either to cull them and let the meat go to waste, or allow them to die in large numbers from starvation. Granted, the ideal would have been to not exterminate the natural predators, except, people have been hunting deer in the American for so long (10,000+ years) that arguably we have long been a natural predator of deer.
Nor do I see a reason to limit things to
subsistence farming – it is well within the means of the average first worlder to obtain a few chickens and raise them humanely for eggs.
Also, it's NOT just a matter of protein. That's a terrible argument, since it's indisputable that people in most of the world (the exceptions being mostly the high arctic) really can obtain all their needed protein from plant sources. It's B
12 that is truly the limiting nutrient.
), and would like to get some decent answers in one place that I can bring up the next time I get dragged into an argument, without spending too much time on it. 
