Empathy

In his books and short stories, Philip K. Dick, often asked what makes make us human. In "Do Androids Dream of Electric", AKA "Blade Runner", the answer he gives is empathy.

The scene that makes it clear, I think, is when the androids tortore a spider. John Isidore watches in horror. A few pages later, Irmgard makes a point about empathy linking all humans. The androids lack empathy, which is why they must denounce it. After revealing the differing agendas of humans and androids, Irmgard immediately switches attention to the spider.

To the androids, the empathy boxes are a threat. They appear link all humans together, but the androids can't experience empathy, and this is why Irmgard asks if empathy really exists. It's almost like a reverse "Invasion of the body snatchers", with the androids trying to save us from some unseen force that controls us. We know the truth, but only because we can experience empathy.

Also note how, when Isidore's belief in Mercer is weakened, and so his support for empathy, he enteres the tomb world. Only Mercer pulls him back. Is Mercer real? This is the question about the spiritual world. The androids have no contact with it, no empathy. For them, Mercer is a fake. Mercer himself admits it, and yet he exists. The androids witness Isidore entering the tomb world - perhaps they too experience it.

I strongly recommend that you re-read the book, or at least chapter 18. It's a classic example of how PKD asked questions about reality and the nature of being human. He used, in this scene, mundane materials like a TV programme and a spider. The news on TV reshapes reality, while the suffering of the spider evokes a sympathetic pain - because Isidore is human.