Why do people ask for slavery ? It will be implemented when goblin (dark) fortress mode will be officially implemented, as was extensively repeated by NW_Kohaku;
And me. In fact, I'm not sure if Kohaku mentioned it.
When it comes to ethics the idea of all dwarves having the same set of ethics is weird. In rl life most humans see cannibalism as horrid. But theres still a minority who practice it.
Fun fact: Most human cultures were fine with cannibalism under certain circumstances, if they didn't outright practice ritual cannibalism. It's just that those cultures which did abhor it happened to be the now-dominant Eurasian cultures.
While cultures will and should diverge, until dwarves OK with slavery happen you shouldn't use that as an excuse to include slavery just yet. Playable goblins may happen first.
I really don't like the ethical argument. Not just because it regards a setting which is easily changed,
Halt.
Toady chose those ethics for his dwarves. They're his dwarves, hence DF dwarves hate slavery.
Moving along now.
but because it really shows a shortage of sound ethical reasoning. Slavery is bad when the alternative to slavery is freedom. That is not the alternative for captured goblins.
In the current situation, here's what usually happens to captured goblins: we strip them naked, and kill them. This is a pretty uniform practice. Sometimes they're tossed down pits so deep that they explode when they hit the bottom. Sometimes they're thrown into an arena and forced to fight dangerous beats unarmed and unarmored. Sometimes they're tossed into spike chambers and repeatedly stabbed. Some people skip the bit where you strip them, and just toss them straight into lava to melt all the sub-steel crap they wear along with their bodies. Some people use them as living training dummies for their military. Some people crush them under bridges.
Is any of that actually less horrible than forced labor?
No, but it's all done by players. I'd bet in-game dwarves would just execute them or stick them in cages for a while like I do.
Don't use players' actions to suggest dwarven tendencies. Any society which did to its citizens what many DF players do would last...maybe half a generation?