Hey, going on for awhile longer with my Greenie theme (I'm even wearing those aptly named 'lesbian sandals' aka Birkenstock sandals currently), here's a green reason for why you and I should be vegetarians. It's all really very simple actually, and it doesn't take a lot of philosophical acrobatics to explain the matter. The truth of the matter is that very many people are going hungry today, and the reason for this is directly linked to our unreasonable demands on beef, chicken etc production.
Check this out, culled from wikipedia - without much further checking, so don't take my word for it and check the claims if you doubt their veracity -: 'the data we had indicated that a beef animal consumed 100 kg of hay and 4 kg of grain per 1 kg of beef produced. Using the basic rule that it takes about 1,000 liters of water to produce 1 kg of hay and grain, thus about 100,000 liters were required to produce the 1 kg of beef.' You can do the same exercise for energy consumption. The bottom line is that the production of beef - even if there were no other reasons against the breeding and killing of animals for food products - is so utterly wasteful and detrimental to our survival interests as a species, it is remarkable that we continue living as we do, and pretending that it's ok. We got away with this wastefulness for a long time, simply because most folks in Africa, Asia and Latin America just couldn't afford to eat the amounts of beef and chicken that the average Northamerican and the average European consumed. Thanks to their growing economies, however, many people have become much better off there. Beef is seen in many of the rapidly developing nations on our little planet as a sign of wealth, so the result is that many more people than ever eat ever more beef. It's highly unlikely that our environment can sustain that sort of thing. So, if you care about future generations of people like you, try to be as vegetarian as you can possibly be.
And, if this doesn't persuade you, here is another good reason for why we shouldn't eat animals anyway, regardless of the environmental impact issue.