Speculative design is a great method to speculate a future or scenario by asking "what if" questions.
Definition:
When is it engaging? What makes it engaging? De/familiarization?
I personally think that dystopian scenarios have a stronger impact than utopian scenarios, because fear is the stronger emotion. If we see a dark future in a movie we see the impact our doing has on the world and what we might leave behind. Utopian movies leave some good feelings behind but we're more likely to forget them because the impression was less strong.