Just because something is heinous doesn’t mean that it won’t make a good story. In fact, the Rule of Drama practically guarantees that it will make a good story. For some weird reason, we humans are fascinated by things in fiction that would horrify us in real life, and love it when our favorite characters are put into situations where we would never want to find our loved ones. Perhaps there are many reasons for this, some of them better than others.
One of the worst situations in which anyone can find themselves is slavery, in which they basically become the property of someone else. Slavery takes many different forms (and has many different tropes), but the thing they all have in common is the denial of freedom, dignity, and the basic human rights that most of us take for granted. So when a character who’s free gets made a slave, you can usually expect to see some pretty high drama as a result.
As the tvtropes page for this trope explains it:
There is often a scene in which the character is being sold on the slave market, showcasing all the evils of slavery; the protagonist will witness how families are torn apart, will have to undress and be examined like an animal, and will perhaps be beaten … If he looks strong, he will be told that he will go to the galleys or the mines — a Fate Worse Than Death — or perhaps to the Gladiator Games. If she (or occasionally he) is attractive, she will be told that she will make a buyer very happy indeed.
If the main character is a slave, this is usually a part of his (or her) backstory; it’s fairly rare for a character to be born into slavery these days, probably because slavery is no longer considered an acceptable social institution in our modern Western society. In older stories, the slave character may be of noble birth, setting up a sort of Cinderella story where they realize who they are and eventually come into their own. That still happens, though usually it’s more about them taking power into their own hands to rise above their awful circumstances.
Surprisingly, this is a trope you’ll see with some frequency in science fiction. Heinlein wrote a novel about it, pictured to the left (one of his better ones, in my opinion). It happens quite a bit in the Sword and Planet subgenre, as well as any gladiator-type tale. You’d think at some point our technology would become sufficiently advanced that we wouldn’t need to enslave each other, but apparently we will use manual labor in the future. Besides, at it’s core, slavery isn’t about acquiring cheap labor–it’s about owning someone, taking away their freedom and control. Until human nature itself changes, we’re probably going to have to deal with slavery in one form or another for the forseeable future.
In any case, there’s something rousing–perhaps even inspiring–about the story of a character who rises above such an awful situation to win back, against all odds, their rights and freedoms. That’s probably why we still enjoy retelling this trope. A character can’t truly rise until they’ve bottomed out somewhere, and as far as hitting rock bottom goes, getting made a slave is pretty dang low.
I’ve played with this trope in a couple of my books. In Sholpan and Bringing Stella Home, Stella goes through pretty much everything on the tvtropes page, which sets things up pretty well for … well, I won’t spoil it. 😉 In Stars of Blood and Glory, Abaqa tries to make the Princess Hikaru his slave, but since they’re both teenagers and he’s younger than her, it ends up being rather hilarious (she gets rescued soon afterward too, so it doesn’t stick long enough for the really bad stuff to happen. And then the rescuers … well, I won’t spoil that either).
Right now, I’m playing with it a bit in Sons of the Starfarers, though I’m not sure where it’ll end up exactly. Probably not so far as this trope, but I never really know what my characters will do–or what will happen to them.