Morality As a Limit
Vegetarianism is an ethical system. It holds animal life to be the standard of good. In this context, vegetarianism does not just mean those that don't eat meat. It is limited to those that do it as part of a particular ethical belief. The belief that it is "wrong" to eat animals.
Regardless of the reason for this belief, it causes an enormous problem for a code of ethics. As a standard of value, it doesn't answer how people should act. It acts as a limit on morality. Since it cannot answer the question of how to act, it relies on a second standard. Two standards, though, make rational choice impossible.
It may be claimed that vegetarianism isn't really an ethical system. Some may just accept it as an ethical principle, part of a larger system. But what system? The only ethical system that cares more about the lives of animals than humans is environmentalism, with its hatred of mankind. If the ethical principle does not conform to the ethical system, than it is immoral.
One claim to support vegetarianism is that it is wrong to kill living entities. This is a faulty induction based on a different ethical code. It can be shown that it is wrong to kill other human beings (under certain contexts). But to expand this to animals is nonsensical. Humans can work together to mutual advantage. They are capable of respecting each other's rights.
Further, if it is wrong to kill animals, why stop there? Why isn't it wrong to kill plants as well? Vegetarians sometimes argue that plants don't suffer. They don't have feelings. But this implies ethics is based on suffering. Under this premise, it would be okay to kill people if they were suffering.
Vegetarianism is a hodgepodge of faulty abstractions, irrational conclusions, and lack of logical vigor. It is a mind killer, though. It is so incoherent, any attempt to integrate it can only result in epistemological chaos. It screams that morality is absurd, and that anyone who takes it seriously is a fool.