But I consider that the matter of defining what is real — that is a serious topic, even a vital topic. And in there somewhere is the other topic, the… - Philip K. Dick

Fake realities will create fake humans. Or, fake humans will generate fake
realities and then sell them to other humans, turning them, eventually, into
forgeries of themselves.

The chamber was an inferno of energy. The figure had completely disappeared. Wisdom waited a moment, then nodded to the technicians operating the cube. They touched guide buttons and the muzzles slowed and died. Some sank back into the cube. All became silent. The works of the cube ceased humming. Cris Johnson was still alive. He emerged from the settling clouds of ash, blackened and singed. But unhurt. He had avoided each beam. He had weaved between them and among them as they came, a dancer leaping over glittering sword-points of pink fire. He had survived.

"We came back [from Mars]," Pris said, "because nobody should have to live there. It wasn't conceived for habitation, at least not within the last billion years. It's so old. You feel it in the stones, the terrible old age. Anyhow, at first I got drugs from Roy; I lived for that new synthetic pain-killer, that silenizine.
And then I met Horst Hartman, who at that time ran a stamp store, rare postage stamps; there's so much time on your hands that you've got to have a hobby, something you can pore over endlessly.
And Horst got me interested in pre-colonial fiction."
"You mean old books?"
"Stories written before space travel but about space travel."
"How could there have been stories about space travel before - "
"The writers," Pris said, "made it up."
"Based on what?"
"On imagination. A lot of times they turned out wrong [...] Anyhow, there's a fortune to be made in smuggling pre-colonial fiction, the old magazines and books and films, to Mars. Nothing is as exciting. To read about cities and huge industrial enterprises, and really successful colonization. You can imagine what it might have been like. What Mars ought to be like. Canals."
"Canals?" Dimly, he remembered reading about that; in the olden days they had believed in canals on Mars.
"Crisscrossing the planet," Pris said. "And beings from other stars. With infinite wisdom. And stories about Earth, set in our time and even later. Where there's no radioactive dust." [...]
"Did you bring any of that pre-colonial reading material back with you?" It occurred to him that he ought to try some.
"It's worthless, here, because here on Earth the craze never caught on. Anyhow there's plenty here, in the libraries; that's where we get all of ours - stolen from libraries here on Earth and shot by autorocket to Mars. You're out at night humbling across the open space, and all of a sudden you see a flare, and there's a rocket, cracked open, with old pre-colonial fiction magazines spilling out everywhere. A fortune. But of co

Fully absorbed in the peculiar text he had become totally oblivious to the noises and movements around him; all that existed for him now was the printed page held motionless before his intense scrutiny.