These three elements are essential for the development of tourism, just as the three elements; accommodation, transportation and agent at the tourism marketing.
People, who cannot protect nature and environment, will not be successful in tourism. Throughout history, humanity settled in the most convenient places for nature and has left their culture there. These places remained to the present with the environment around, and today tourism is created by visiting, experiencing, staying and living those places.
When reasons of natural disasters, natural events, climate and atmospheric changes are examined, it is very obvious that people are the most important factor.
Think of the damages of volcanic ashes, floods, tsunamis... etc. to world environment. Reasons of those damages are mostly caused by humans that cannot protect environment.
If we cannot protect environment around us, we cannot make tourism.