He's not a kid, he's an adult much older than me with a family.
In any case, I meant to mention that in my first post, but I totally forgot to. Then I was going to go back and add that, but I forgot to do that, too.
The reason are really two-fold, though. The first is health. Meat isn't good for you. Meat consumption has been linked to various forms of cancer, heart disease, and other nasty stuff. Not to mention that the majority of saturated fats, cholesterol, and other bad stuff come from dairy and the like. The main benefit to meat and dairy is the vitamins and minerals you get from them, but those can be consumed in different ways that, although they aren't as efficient, they are healthier.
The second reason is ethical. I mentally evaluated my beliefs about animals. Am I ok with animals suffering for me? Dying for me? I'm upset when my dog or cat dies, but not the cow that fed me. Does that make sense? What's the difference between my dog and a cow/pig/chicken, other than familiarity? I couldn't resolve that question in any meaningful way. A lot of people imagine farms as ideal places where animals wander around and stuff, but 80% of the meat in Canada (and probably more in the US) come from factory farms and feedlots. In those situations, animals are treated extremely badly. Dairy cows and egg chickens and such are treated basically the same as the meat animals, and the ones that don't produce enough are simply killed off and fed to the others. When I was at the Calgary zoo, they had buckets of dead baby chickens (the male ones, whatever they're called) to feed animals. They said that they came from chicken farms and that they're of no use since they don't lay eggs, so they're just killed.
I'm aware that this doesn't happen everywhere, but the first part of my paragraph holds, in my mind -- what's so special about me that it's ok for other living animals to die just for my pleasure? I consider that selfish.
In addition to those two main reasons, there are a lot of good facts
here, including environmental reasons, monetary reasons, etc. Those weren't big concerns in my mind, but they're definitely worth looking at.
The main influence of my friend who did it was showing me that it's not a difficult lifestyle to live. Before I knew him, I assumed that it was an extremely difficult lifestyle to maintain. After seeing him do it, I realized that it was a pretty easy lifestyle, as long as you don't mind giving up things like fastfood. So there you go.
Also note that I'm not trying to start an argument, and that this decision isn't up for debate. But you asked for the facts, so there they are.