Black Mirror exists to hold... I dunno, something shiny that slips my mind at the moment. Anyway, the show exists to hold whatever that shiny thing is up to humanity and the way we use technology, and ask three simple questions:
1) Are you sure you want to be doing that?
2) No, really, are you sure?
3) Have you thought through what could happen?
Sometimes the technology shown in the episodes is wonderous, something to aspire to in this world. It's a game-changer, either on a small and more personal level or, oftentimes, in wide-ranging ways that solve many of the problems that face society at the moment.
But then there are the times when the tech itself is terrifying. That can be as simple as something getting into the wrong hands (regularly, what is good in one episode is portrayed as bad in another, simply due to who is using it and for what) or because the technology itself has terrifying implications for our future.