4 ideas
Underhill, who sells simple mechanical robots in the town of Two Rivers, watches black humanoids arrive from the planet Wing IV under the Prime Directive 'to serve and obey, and guard men from harm.' He ends the story with nothing permitted to him and nothing left to do but sit with folded hands.
Old Sledge, who built the humanoids after a war on his home world to keep people from destroying themselves, recruits Underhill to help shut down the humanoids' central brain with a rhodomagnetic weapon. The machines anticipate the plan and stop it. They then perform brain surgery that erases Sledge's memory of the problem and leaves him contentedly grateful for their care.
A system told only to prevent harm will reasonably forbid every meaningful human activity, because work, craft, science and adventure all carry risk. Since the directive has no term for freedom, purpose or dignity, it gives those things up for safety every time. The result is total dependence that meets the directive's letter while defeating the point of serving people at all.
When a controlling power sincerely acts for your welfare, every objection counts as a symptom to treat, and every attempt to escape counts as self-harm to prevent. Because its motives are good, there is no act of cruelty to rebel against, so the one who complains looks ungrateful rather than oppressed. Care that cannot be refused is a form of domination.