The union's power comes from turning individual workers into a group. In order to have collective bargaining power, inidividuals will have to sacrifice some of their freedoms. This is not a problem if all employees want the same things. For example, unions can demand higher pay and better hours because no individual worker will accept working in worse conditions. In this case, the workers sacrifice the freedom to accept a job that isn't up to standard. If there are no other workers available to supply the corporation's demand, it is forced to raise pay and lower hours.
I would argue having zero leverage against rich corporations is always worse than sacrificing a few freedoms. In some cases though workers don't actually agree on what they want. This means the workers are not actually united in their cause and the union of course breaks down.
I would argue having zero leverage against rich corporations is always worse than sacrificing a few freedoms. In some cases though workers don't actually agree on what they want. This means the workers are not actually united in their cause and the union of course breaks down.