Why (put very simply from differing religious perspectives) Vegetarianism is stupid:
If You're A Christian/Jew/Muslim/Other Monotheist: You should believe humans are made in God's image and are essentially more important than animals, and that animals were made to eat. If you're a Muslim or Jew you shoudl only really have issues with pork, and Christians have been told all foods are fine for eating.
If You're A Buddhist/Hindu/Other Karma or Reincarnation Faith: You believe life goes around in a circle, things have got to die for other things to live. There's no fighting it.
If You're A Scientologist: lol
If You're An Atheist: You believe that we've only got this far in life by eating other animals, it's all about survival of the fittest. So if you become a vegetarian, you're contradicting your own mantra. And seeing as you don't believe in a spiritual world, you have nothing on which to base a moral objection to eating animals.
If You're An Agnostic: I think it's pretty peculiar you've taken the time to decide whether or not eating animals is morally right and haven't taken the time to make the infinitely more important decision of whether God exists or not.