No matter which party or politician backs a particular piece of legislation, its advocates nearly always proclaim that it serves the public interest. And opponents are just as quick to claim that the legislation is harmful to the public interest. The Keystone XL pipeline serves as an example.

For years, the pipeline was a controversial issue. Critics claimed that the pipeline did not serve the public interest. Jane Kleeb, president of the Bold Alliance, one of the Keystone XL’s leading opponents, told the Nebraska Public Utility Commision, “We have the evidence on our side that this pipeline does not meet the public interest of Nebraska.” Proponents responded that the pipeline would reduce dependence on oil from the Middle East and create jobs—both of which it argued was in the public interest. Union members favored building the pipeline.

But attorney Brian Jorde said, “The main question is not farmers versus union members. We also support union members and jobs. The threshold question is: Is this project in the public interest of Nebraska? And it’s not.” Which side is correct? Is the pipeline in the public interest or not?

While both sides bickered over what is and isn’t in the public interest, neither bothered to define what constitutes the public interest. And Keystone is hardly the only example. The reason that nobody bothers to define the public interest is quite simple—the term can’t be defined.

The American public consists of more than 330 million people. Some are gay and some are straight. Some are male and some are female. Some are white and some are Hispanic, black, Asian, and other ethnicities or races. Some are Christian, some are Jewish, some are Muslim, and some are atheists. Some like baseball and some like ballet. In short, the American public is not monolithic. It consists of individuals with a wide range of characteristics, values, and interests. To proclaim that a particular policy or program serves the public interest is to ignore this vast diversity of values and interests.

In practice, the public interest means that the interests of some individuals take precedence over the interests of others. Some individuals will be forced to sacrifice for the alleged benefit of others.

It is not surprising then, that groups seek to curry favor with politicians and bureaucrats. Groups seek to influence the policy makers who wield tremendous power over individuals and businesses. Those groups want favorable legislation and regulations, and they are willing to trade political support for those government favors.