Let me begin by saying that I do not mean this node as an attack on vegetarians, or on vegetarianism in general. Also, I will not address the morals/ethics of vegetarianism here. I don't care about your opinion, so why should I make you listen to mine? (hhos) Although I am a practising omnivore, I have never felt any need to make others eat meat. However, I am quite bothered by ignorance and FUD, so I would like to clear something up.

Many vegetarians cite healthiness as a primary reason that they choose to be vegetarian. This is not valid. Although it is certainly possible to create a vegetarian meal that is healthy, not all vegetarian meals are healthy, many non-vegetarian meals are healthy, and it is, in general, more difficult to maintain a healthy diet while excluding meat.

Meat fills an important part of the human diet. It gives us necessary nutrients, primarily protein and iron. It is possible to get protein from other sources; however, the vast majority of vegetable proteins are not complete proteins, forcing the body to expend energy creating complete proteins, generating toxins (ketones) in the process. And of course, this means that vegetarians need to take care to eat the right combinations of foods to get the right combinations of partial proteins (or at least they should - many get by with ignoring this, but it is not healthy). Iron, on the other hand, can easily be gained from many vegetables (almost anything green). Unfortunately, most vegetarians still do not seem to get enough. Vegetarian women, in particular, need to be very careful about getting enough iron, as this is a bigger problem for women than men to begin with.1

Not all meat is a fat-loaded 18-ounce butt steak.2 In fact, most meat is not unhealthy at all. First of all, even the things that are called generally labelled "bad" (e.g. fat, cholesterol) are in fact needed by the body. There are numerous myths surrounding these, as well. In the interest of brevity, I will simply state that a) even if you don't eat any fat, your body will generate it (along with some nasty ketones), because it needs it, and b) there are two types of cholesterol; the good kind helps fight the bad, and your body actually needs some of both. For most people, even the less healthy meats like steak and bacon3 are perfectly fine on occasion. Unless your doctor tells you differently, you can probably eat these in moderation without having a measurable effect on your overall health. But even aside from this, there are many meats which are quite healthy. A boiled chicken breast is very healthy, and fish contain oils which actually fight "bad" cholesterol (this is that "good" cholesterol).

So when it comes down to choosing a meal, arbitrarily cutting out meat greatly restricts the options for healthiness. Figuring out what combinations of beans will give you a complete protein is much more difficult than simply tossing in a small chicken breast. A simple green salad is not a healthy meal, but a simple green salad with some tuna on top is closer.

In case you're not convinced, I'd like to show a simple diagram. I haven't done ascii art for a while, so please bear with me.
####################################
#            OOOO                  #
#         OOO    OOO               #
#       OO          OO             #
#     OO              OO           #
#    O                  O  x       #
#   O                   xO    x    #
#  O                  x   O     x  #
# O                        O       #
# O                  x     O     x #
# O                        O       #
#  O                  x   O     x  #
#   O                   xO    x    #
#    O                  O  x       #
#     OO              OO           #
#       OO          OO             #
#         OOO    OOO               #
#            OOOO                  #
####################################
The large square represents the universe of all meals. The circle of O's represents the set of all healthy meals. The circle of x's represents the set of all vegetarian meals.4 Note the space within the O's, but not within the x's. This is the set of all healthy meals which do include meat. By arbitrarily excluding meat, one removes all of these meals from their diet. It is the existence of this area that shows that vegetarianism is not, in and of itself, healthier than a diet including meat. A healthy diet can be made either way. Those concerned about their health should choose their diet on the merits of each food individually.

1Do you bruise easily? This is a likely sign that you do not have enough iron.
2There was a comedian who used to use "18-ounce butt steak" as a catch phrase. He was very funny; I wish I could remember his name.
3Personally, I eat bacon almost every day. Then again, I have no intention of living beyond thirty.
4I made the O's set larger because any given healthy vegetarian meal can easily be made into more than one healthy non-vegetarian meals through addition of meat. Both sets are, in fact, infinite, and the relative size does not affect the logic.