Where do libertarians stand on cartels? Are they free to form them? If so, are workers not free to form them, too? Are consumers free to form cartels with their own enforcement arms? (We call the latter "governments.")

There's just no logic to the idea that people are free to do whatever they want other than combine to keep people from fucking them over. Mr. Nozick's disciples needn't worry. If the mob does them any harm, they will be compensated. What more could anyone ask?