You see, it's really quite simple. A simile is just a mode of comparison employing 'as' and 'like' to reveal the hidden character or essence of whatever we want to describe, and through the use of fancy, association, contrast, extension, or imagination, to enlarge our understanding or perception of human experience and observation.
Too many cars, too many factories, too much detergent, too much pesticides, multiplying contrails, inadequate sewage treatment plants, too little water, too much carbon dioxide - all can be traced easily to too many people.