George Carlin "...immune system is to kill germs. It needs germs to practice on ... When i was a little boy in 1949 we swam in Hudson river. The Hudson River was loaded with raw sewage. That's right, we swam in raw sewage. You know, to cool off. ...":
Edit: imagine, theoretically, if there is no germs and no need for immune system, would it mean additional biological resources available inside the human body for something else, like for bigger/better brain, etc...?
Tragically, it would - and in the non-hypothetical world, probably does. There is a fair amount of research showing significant cognitive development improvements when replacing dirt floors with concrete ones.
Yes, the immune system would probably be culled from our genome eventually if there were no pathogens left.
It would be tremendously risky as a species, and also very unfeasible considering how important microbes are to life, but you are correct in expecting an unused "feature" would likely be removed, as every "feature" has a cost. Much like cave fish that live in total darkness all their lives- their eyes disappear...
http://www.youtube.com/watch?v=CnmMNdiCz_s&list=PL4DDBE51446...
Edit: imagine, theoretically, if there is no germs and no need for immune system, would it mean additional biological resources available inside the human body for something else, like for bigger/better brain, etc...?