Riasi: In any event salle-Korsa was kind enough to allow me to download the pig slaver’s data files before blowing him to quarks. I would have liked to keep him alive for questioning at least but salle-Korsa was pretty clear on his desires. I did not care to argue with him. For a pirate he has a strong sense of honor in some things. He’s a good tipper too, I hear.
Captain: So you downloaded the data from the slaver and found this list? Confederation citizens posted by name. Data files for each. It looks like someone was planning mass abductions event.
Riasi: I would say so. There are a large number of beanpoles listed, some frogs, several humans, one vole female and child.
Captain: I can relay the names to my superiors and alert the security forces. Meanwhile we can see whether the targets fall into any patterns.
Riasi: That would be good Tesla-Captain. Apparently my colleagues and I were not on the list. We were just a stop along away. Rather insulting being the target of impulse buyers.
Captain: Or flattering. If I’m reading these prices right.
Slaves, one of mankind's oldest institutions is a staple of space opera/pulp. This is often decried by people who prefer hard science fiction. Robots or at least automation are going to be way cheaper and more practical. Here's some doubletalk to allow you to make oppression an ongoing theme in your game. After all where there are the oppressed there are also liberators. There's too many good story hooks here and slavers of any stripe never go out of fashion as villains. Any comments about me defending slavery will be deleted.
Why not a robot?
1) Robots require charging, parts, servicing and other commodities not available locally. Sentients require the same foods and care the oppressors require.
2) Slaves are a status symbol (very important among your proud warrior races).
3) A slave revolt is bad enough. A robot revolt is an economic blackhole. Plus slaves are way easier to keep complacent ("We'll give you basic cable if you get back to work now ... okay, premium.")
4) Slaves have some quality that can't be built into robots. Adolescent power trips aside, a clairvoyant or even a skilled artist might be worth their weight in AI chips.
5) A debt. Indentured service is a form of slavery. New colonists might be forced into indenture before being allowed to settle to give the colony an economic boost.
6) Social norm. The masters come from a caste culture with slaves. there have always been slaves. That's it.
7) Responsibility. Back to the proud warrior race. You conquered them, you're responsible for them.
Finally in a SF setting there are a few other considerations. As mentioned above automation is the enemy of slavery. So your SF slave is more likely to be an oncologist or geophysicist than quarry worker. In the Roman Empire having slave teachers for rich citizens' children was not unheard of. Similarly the Mongols often carried off craftsmen after looting a city, those having skills the nomads lacked.
Your proud warrior race might have slaves servicing their battle fleet and weapons. Raymond McVay had this to say:
Lastly SF provides many high tech alternatives to the whip to enforce servitude: psionics, drugs, neural weapons, and brain implants are just a few of the atrocities possible. They work great until they don't then you have an adventure.
For the truly twisted you could have an enslaved population building robots for export offworld. Who's going to to rebel first?