If the design and engineering of a mass produced product is bad: recall, or other remedy. All the samples are bad and share the same fault.
If the design and engineering are up to snuff, but production tolerances are loose, quality control is faulty, and the engineering of the line is overly optimistic, you get sample defects, aka lemons.
Humans will make errors. A lot has to do with the workplace and how it is set up. With good cooperation between management, engineering, and labor you can get quality improvements - the old Japanese miracle method
Labor unions are not a one sided thing - they became necessary due to management approach and attitude towards workers. Defects are the fault of management that isn't paying attention to the details as much as it is the fault of the worker.