Because basically there isn't really any argument against vegetarianism. From everything I've read, it's at-worst a perfectly acceptable lifestyle choice. At best, it's the smart move to make, whether for ethical or health reasons. (And please realize that I'm not talking about vegans. That seems to be another story which I haven't researched enough.) It's my understanding that there are a few things that vegetarians need to consider when it comes to staying healthy, but it's not enough to make a big deal about it or be a deterrent.
So why am I not a vegetarian? Well, I like meat. A lot. I did an experiment where I went a month without eating meat, and while it was actually kind of fun for the first couple of weeks, I quickly grew tired of it. I considered doing it again, but my wife wasn't on board, and I'm the one who does all the cooking. It's funny because she tends to eat less meat per meal than I do, but she's gotta have it maybe even more than I do. As for my son? The boy loves chicken, and he'd probably start to get on me about giving him a grilled cheese sandwich every single night. (Your choices are already limited when you have a three year old - although tonight he happened to eat nothing but carrots and a bit of salad for dinner.) While I suppose that I could stand to have at least a few vegetarian lunches per week, I'm also too lazy to make two different meals each night. One last issue is that when I eat less meat, I tend to eat more carbs, which isn't really good for me either.
A secret part of me hopes that when he gets older he'll make the ethical choice to go vegetarian. I don't know if that would necessarily force me to become vegetarian, but I would completely support him and help him in any way that I can, which would probably naturally result in myself eating less meat. I don't know though - did I mention that he loves chicken? Normally when I cook, I'm cooking for two and a half people. When I make chicken, he packs away enough that I have to make enough for four people. (I'm exaggerating...but only a little.)
So, are there any arguments against vegetarianism? I can only think of a few, and these aren't against vegetarianism in general but against some of the more extreme comments that I've heard in the past. I'm going to assume that these views represent the minority of vegetarians.
One attitude that I've gotten from (just a few) vegetarians is this idea of: "How could you even do such a thing as eat meat?" You know, like it's this new fad that just started recently. The fact is that human beings have been eating meat for a long time. Not only that, but eating meat led to our brains developing the way that they did. What this means is that eating meat is what made us human to begin with. The irony of this is that had we humans never eaten meat, we would have never been able to advance to a position where we could make a choice about whether we eat meat or not.
There was a show on the National Geographic Channel that I was watching where a suburban American family lived among an indigenous tribe in Central America. (I think that they were in Panama, to be more specific.) The mother's vegetarian sister came for a couple of days and criticized the fact that the people there were eating a chicken. You know, because they could have just gone down to the local Whole Foods in the middle of the frikken' jungle and picked up some perfectly acceptable soy substitute! Again, I'm sure that most vegetarians realize how silly this is, but the fact of the matter is that if society completely crumbles and we have to resort to a hunter/gatherer, then you'll be a damn fool to not eat meat.
I don't remember the precise details, but I have a coworker whose significant other is a vegan. However, when she went to Africa (don't remember the exact country - we're talking sub-Saharan though) she ate goat. Why? 'Cause otherwise she'd starve! I'm hoping that she represents the majority of vegetarians and vegans who realize that their lifestyle is a luxury that's afforded to them by modern society. Sure, there might be some exceptions, depending on what part of the world we're talking about, but overall that's pretty true.
So yeah, vegetarians, you win. You guys are right. But if your prehistoric ancestors made the same choice as you, you wouldn't have been able to make that choice. (Did I just blow your mind?)