Absolutely agree with everyone about cleanliness and immunity. The body is not designed to live in a sterile environment because immunity against various things is strengthened only when they are exposed daily. In fact, living in too sterile an environment may be the trigger for auto immunity or an unregulated immune response (where you become highly sensitive to outside triggers).
However, we are not talking about organic bacteria/viruses/single celled organisms that can be killed by the body's immune system. We're talking about chemicals that are toxic in built up doses. If you chuck a spoonful of lead in your soup every now and then in the hope that your body may build immunity to it, chances are you're going to die from lead poisoning well before that ever happens! The kidneys and liver are the first port of call for flushing toxins out, so they will be overburdened, and whatever toxins are not flushed are stored in the body in fatty deposits. And like Molly says, chemicals do affect your body eventually. So whether or not you are against the organic movement, you can't deny that eating pesticides (for eg) daily in small doses will eventually affect you, not to mention the creosote in the soil and whatever else.
