A city council has proposed banning disposable plastic bags in all retail stores and requiring shops to charge for reusable bags. Environmental assessments show that plastic bags constitute a significant portion of street litter and cause harm to marine life when they enter waterways. The council cites evidence from cities that have implemented similar bans, where plastic bag usage dropped by over 80% within the first year. Reusable bags can be used hundreds of times, dramatically reducing overall bag consumption. Local environmental groups have endorsed the proposal as an important step toward reducing plastic pollution. The ban will therefore significantly decrease plastic waste in the city. Which one of the following is an underlying assumption of the above argument?