Vegetarians are people who don't eat meat or fish. There are other variations of this diet, namely pescetarians, who eat no meat but fish, and vegans, who eat no animal products at all.
People who think that vegetarianism is a good idea argue that it is cruel to breed animals in mass production factories, or that it is unhealthy for us to eat so much meat, or that it is bad for the environment.
People who oppose vegetarianism say that it is natural for us to eat meat, and therefore we should. They say that our body needs the nutrition that meat gives us, and we shouldn't live without it. They say that it is not unethical to kill animals, because it is natural that some animals eat others.
I think that both sides have good arguments. While I enjoy eating meat and think that it is good for our health to consume moderate amounts of it every week, I agree that the way animals are bred in our society nowadays is cruel and unethical. I would rather reduce the amount of meat I eat and pay more money for it, so that farmers can afford to keep their animals in better conditions, than continue the production as it is now.