Apart from the obvious political justifications (people want the union vote) there are some sound reasons why unions are different from cartels like the employe

Apart from the obvious political justifications (people want the union vote) there are some sound reasons why unions are different from cartels like the employers in the article are alleged to have formed. A cartel is several companies colluding to raise prices above/below the market price. A labor union might be though of in the same way, but in practice is is very hard for a union to really control the supply of labor, because it is made up of thousands of people. It is only when they are tacitly allowed to use force/violence that unions can effectively prevent strike-breakers. So given how ineffective they are at permanently raising wages (perhaps they raise wages a bit, but not nearly as much as if they had a true monopoly), unions should probably be allowed since if people choose to join them, they must provide some other benefits, such as representing individual workers with grievances, etc.