And so bacteria, parasites, and viruses. They do it for survival, even though it serves no purpose to others. A human has as much purpose (or maybe even less) as a bacteria/ parasite/ virus. What these small organisms do is in fact control the population of humans and other fauna. Just think about it, disease is one of the most effective population controls. Without it, we would be even more over populated than now, and there would not enough ethical and ecological living space for humans. It may sound cruel and un-ethical, but it is a sad reality, disease and parasites are a natural population control for us. I personally think one day, disease will out run modern medicine and start a large pandemic wiping out the majority of the population, probably when we are over crowded. Just my 5 pennies.