Why is the Imune System essential?

Question: Why is the Imune System essential?
- Keywords:
  immune system
Asked by saras to Carmen, Daniel, Laura, Noel, Steph on 9 Mar 2015.
- Carmen Denman answered on 9 Mar 2015:
  
  Ever heard of bubble boy?
  
  http://en.wikipedia.org/wiki/Severe_combined_immunodeficiency
  
  If we didn’t have an immune system, we wouldn’t last long, and in order to survive we’d basically need to live in a sterile bubble away from any little thing that might make us ill.
- Noel Carter answered on 9 Mar 2015:
  
  The best explanation is seeing the effects in people without one. A series of diseases known as severe immunodeficiency disease or SCID.
  This Wikipedia page is quite a good intro
  
  http://en.wikipedia.org/wiki/Severe_combined_immunodeficiency

Question: Why is the Imune System essential?