I watched Fast Food Nation the other day (a pretty good movie that I would recommend for a person in the right mood) and got to thinking a bit about vegetarianism. The movie ends with what is supposed to be a terrifying and awakening look at the process by which a cow is killed, cleaned, and packaged for consumption. The gore is successfully off-putting, but a few minutes after the dramatic revelations of the killing floor's horrors (it's not really a floor, it's more of a steel grating that allows material to slide through so it can be collected and exported) I got the feeling that I'd been strong-armed.
The elements of the scene that make it shocking and persuasive are the sheer size of the beasts, the dramatics of the blood, and the enormous supply of cattle waiting to be butchered. The scene definitely has an effect, but in less emotional retrospection, I realized that none of those elements alone should persuade someone towards vegetarianism, except for in two special cases which I will consider below.
Before I get to those two cases, let me defend my claim that nothing about the killing floor should prevail on a principled acceptance of eating meat. If you condone killing animals for food, there should be nothing about the size of the animal nor the gore with which it is slaughtered that should dissuade you from that belief. I like to catch and eat fish. In between those two stages, I have to kill and clean the fish. There is a little blood and guts involved in that, but nothing to make you too squeemish. But, if you watch Fast Food Nation and see how cattle are butchered, there is plenty to make you squeemish. In function, the two processes are exactly the same: you are killing something for food. Absolutely nothing about the size of the animal, nor the quantity of blood, nor the squeemishness of your response changes the morality or ethics of the act. If you are on board for cleaning a fish, I don't see any reason why you shouldn't be on board for killing a cow (beyond utilitarian concerns like effect on the environment and efficient use of resources and things like that). Trying to scare you out of your moral judgments with blood and gore is a ploy.
Except for two cases. First, if you are sufficiently horrified by seeing the butchering of an animal such that you believe you could not kill the animal yourself, then the honest thing to do would be to embrace vegetarianism. If you could not kill the thing yourself, it is not fair to ask someone else to do it for you. This does not mean that you have to personally kill everything you eat, but you should be prepared to do so in each case. If the only thing preserving your ability to eat meat is your distance from the killing act, then I think you have to bite the bullet and give it up.
Secondly, you could reject the premise that one is ever justified in killing an animal for food. If you make this move, then you can absorb the claim that the size or nature of the animal doesn't matter and still denounce the killing of cattle, as Fast Food Nation would probably have you do. This is an attractive move because it seems to simplify things neatly for you. If you reject the killing of animals lock stock, then you don't have to worry about making distinctions between the morality of killing this animal vs that animal and you don't have to worry about who is killing the animal or how or how many of them or any of those considerations. However, I think this position leaves you with a huge philosophic debt: that one finds it very difficult to account for the special nature of consciousness (like most of us would like to do) if one refuses to make any moral distinctions among living things. If I draw no distinction between treatment of cows and treatment of people, then what philosophic grounds do I have to regard cows with different ethical status than people (like I presumably want to do)? This is what Buddhists do. But if you do not want to be a Buddhist, and you do not want to make any distinction between living things when it comes to ethical treatment, then you are left with quite a large philosophic problem.
There's a lot more to the philosophy of vegetarianism, and a lot of it is pretty interesting. I am not arguing for it or against it here. I'm merely pointing out that if you find the killing of animals morally defensible, then neither the size of the animal nor the gore associated with its killing should dissuade you from that moral judgment. One would be well served to keep that in mind should one watch Fast Food Nation.