We're losing our arms race with our only predator. By misusing antibiotics, diseases are evolving and becoming immune. Basically, diseases are evolving and we're not. We need to be careful.
Here is a link regarding diseases, antibiotics and evolution. It's cool if you have faith in creationism, but the fact of Evolution and the idea that we're "not playing" (because our environment is too clean) could be the end of our species. I apologize for being dramatic.