If the post title wasn't enough, let me say here there are all kinds of spoilers in this post.
Most of the episode takes place in a virtual world. When you die, your consciousness can be uploaded to the computer, and you can live approximately forever--or as long as you like--in the simulated world.
White girl, quintessential mousy 1980s type, is roaming the simulation in 1987, meets black girl who's there to party; they fall in love. Drama ensues. Elderly black woman marries the elderly white woman in real life, white woman dies and gets uploaded. Black woman dies sometime later and also gets uploaded. Cue "Heaven is a Place on Earth" as we see the server racks full of uploads. The link above gives more detail but that should be enough for our purposes here.
The usual tropes are hammered here. Lesbians, of course. Atheism. Gay marriage, and the trivialization of marriage. Free love. Human euthanasia. Never-ending youth in a world completely free of consequences. It's a perfect commie-lib world! Of course this episode was critically acclaimed, and GLAAD loved it to pieces.
I've said before that all the settings in Black Mirror are dystopias, and this episode was not an exception. "But it has a happy ending!" You say.
No, it doesn't.
First off--the virtual world is nothing but a neverending party. We're never shown anything else--no one building or creating anything, no art or music or writing or anything. No world-class scientists, able to continue their important work long after their physical bodies have perished. Nothing.
Humans are not built for that; given over to idleness, we turn bad pretty quickly. Someone in that simulation would rapidly get bored and begin doing all kinds of reprehensible things. It seems that people can't be injured or killed in the simulation, so murder would be out, but in the scene where the female lead "Yorkie" (the white girl) visits the ultra-kinky sex club we see people doing BDSM and hearing a woman's voice cry out in pain, so people can be hurt, can be made to feel pain strong enough to elicit involuntary cries, in the simulation. So what's to stop someone, bored with everything else, from deciding that torture is the hobby to try? To say nothing of what happens if someone outside the simulation decides that things are too perfect in the sim and it needs more horror, disaster, pain, and suffering.
But that pales in comparison to the second thing.
Second--what if they're wrong? What if there is an afterlife, which by definition can't be detected with scientific instruments? People still die--that is, their bodies die--but their souls can't be captured by a machine and uploaded, so that instead of the actual person being in the simulation, you have a computer simulation of the person in the simulation.
The real problem here is the philosophical problem of what consciousness is. If consciousness is just a pattern of electrical charges, then it doesn't matter where those charges are stored and a computer chip is just as good as a brain is. But if it's not--
Being, as I am, a Christian, there are tenets of my faith which guide my philosophy. That includes this matter, and so I take the view that no, you can't capture a person's soul and upload it to a computer. At most, technology could capture all the information in a person's brain, but that wouldn't be the person himself, kind of the same way a shadow isn't the object casting it. You could probably gin up an OS which could use that information to provide a simulation of the person, but it wouldn't be that person.
But it gets worse. If the souls can be captured and uploaded, then all you have done is to make hell a place on Earth.
Hell is a place outside the beatific vision, someplace removed from the presence of God. If Billy Goodguy led a pious life and is destined to be with God, but someone uploads his soul to a computer bank, Billy's outside the beatific vision and is denied being with God. That's the very definition of being in hell.
The world presented in this episode is a dystopia at best because it leaves millions of peoples' consciousnesses at the mercy of whoever has root access to the computer system. Suppose the corporation running the thing decides they can make lots of money by using those consciousnesses for running things and solving problems? It's not slavery; they're bit patterns in a computer and the people they came from are dead, and the dead have no rights. The fact that those bit patterns are conscious and can feel pain is useful, because that way you can train them to do what you want them to do. (This point is made very well in another episode of the series, White Christmas, where they routinely enslave copies of peoples' consciousnesses.)
But at worst, the world presented in this episode is satanic--and that's not a word I throw around lightly. You think it has to be fire and brimstone to be hell? Think again; all it has to do is keep souls destined for salvation out of heaven to be hell. That's all it takes.
And that's why I hated this episode.