In the book Do Androids Dream of Electric Sheep? it is never clear why the androids were banned from Earth, but kept legal on the colony worlds. That is my only problem with the book. Is it prejudice that the humans on Earth have that they don't have on the colony worlds? Or is there a history of android aggression on Earth? Are the humans on Earth mad that they don't have androids like their counterparts on the colonies do? Does anyone know/have any ideas?
Earth is dying, and the U.N. is actively trying to get everyone to emigrate to colonies and a personal android for colonists is part of the incentive to go.
That had been the ultimate incentive of emigration: the android servant as carrot, the radioactive fallout as stick. The U.N. had made it easy to emigrate, difficult if not impossible to stay.
If androids were available on Earth, that incentive would be less effective, which is one reason they are illegal.
Furthermore, since androids were forever in the service of their masters, an android being on Earth implies that it has committed murder to get away.
For Rick Deckard an escaped humanoid robot, which had killed its master, which had been equipped with an intelligence greater than that of many human beings, which had no regard for animals, which possessed no ability to feel emphatic joy for another life form's success or grief at its defeat — that, for him, epitomized The Killers.
This is necessary. Remember: they killed humans in order to get away.
The androids do not have empathy and express no regard for life, which means they are a threat the already endangered surviving species on Earth.
Pris clipped off another leg, restraining the spider with the edge of her hand. She was smiling.
Finally, it is suggested that the androids, particularly the new Nexus-6 models, are a threat to mankind as a whole, and tracking down free androids is necessary to prevent them from forming a sustained rebellion.
These Nexus-6 types . . . they'd roll all over us and mash us flat. You and I, all the bounty hunters — we stand between the Nexus-6 and mankind, a barrier which keeps the two distinct.