Often people feel morally obliged to avoid doing something for the common good. But as soon you charge a fee people will assume that that fee reflects the soci

Often people feel morally obliged to avoid doing something for the common good. But as soon you charge a fee people will assume that that fee reflects the social cost and maybe start doing it a lot more. http://freakonomics.com/2013/10/23/what-makes-people-do-what-they-do/ http://freakonomics.com/2013/10/23/what-makes-people-do-what... Either don't charge money for something and use suasion to get people to use too much or charge enough that you're happy that they use as much as they can afford.