The labor force is full of cartels, and members of labor force cartels earn more money because of their increased bargaining power with respect to either their employers or the public. If you don't know what I mean by a cartel, then read the Wikipedia article which defines a cartel as "a group of formally independent producers whose goal it is to fix prices, to limit supply and to limit competition."
The most obvious labor force cartel is the labor union. Workers band together and bargain collectively. It works pretty well, because unionized workers often make twice as much money as non-unionized workers doing the exact same job. Unions aren't limited to blue collar guys; actors have a union, and Ronald Reagan was once its president.
Cartels are common in higher paid professions, they are just less obvious than blue collar labor unions. One of the more obvious professional cartels are medical doctors. They are able to limit entry to the profession by limiting the number and size of medical schools, and by ensuring that the path to medical doctor is a long and grueling ordeal.
Some cartels are best identified by the fact that their members make so much money. Take investment bankers. They make huge amounts of money. Everyone wants to be an investment banker. All they do is prepare some charts and graphs using Microsoft Excel. It's nothing that special. Investment bankers have created huge barriers to entry to their profession, and at the same time they have a gentleman's agreement to never compete on price--they always charge 7%. What exactly are the barriers to entry? They only hire people with MBA's from elite schools like Havard, Wharton, or Columbia. They also make new associates work extremely long hours. Why don't they just hire more associates so they don't have to work as long? Because then there would be more people who know how to do investment banking, and the eventual result would be lower salaries for everyone.
Within the legal profession there is a cartel of high paid BIGLAW lawyers, and they use the same restrictive hiring practices as the investment bankers and also have a gentleman's agreement not to compete on price. They also make associates work long hours in order to minimize the number of people with BIGLAW work experience. Lawyers also have a lot of protections for their profession encoded in the law; one of the most interesting is that it's illegal for lawyers to perform legal work for clients if they are an employee of a non-lawyer. This sets them apart from every other profession.
College professors have a great cartel going. Besides the requirment of having a PhD before one can join up, they engage in the same restrictive hiring practices as investment bankers, and they have a tenure system which ensures them lifetime employment. There are zillions of people with PhDs who can't get a job as a professor because of the college professor cartel which restricts hiring. If the profession were open to everyone with a PhD, the salary of professors would decline to practically nothing. So it's massively hypocritical when college professors complain about labor unions when college professors are so much better at doing what labor unions do.
If one guy makes a lot more money than someone else, there's a good chance that the wage differential does not mean the higher paid guy is contributing more to the economy--it just means the higher paid guy is in a cartel.