Romans disagree. While legally slaves where only objects ethically there where unwritten rules that slaves are humans too and you should treat them like familly too and that you should release them after ten to 20 years of servitute.
Oh and the infamous mining slaves where no actual slaves as those where way to expansive. Instead there where used the equivalent of a modern wage slave because it is much cheaper and easier to replace a free plebejan or the son of one.
That's a very revisionistic take on slavery in rome. Of course you had people who treated their slaves not too harshly (even though I believe this notion is basically just due to Seneca telling people to treat their slaves with respect) - but in the end they were still property. Especially at the height of rome's power, after the punic wars for example, the influx of slaves didn't do their conditions any good. They were basically a dime a dozen.
The part about mining slaves is not true either. I recommend 'The Roman Near East' by Fergus Millar; it gives some insight about slave labor in mines and why it was basically a death sentence. A more graphic description is found in Eusebius' account of the treatment of slaves in Chapter VII of this article:
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Which is irrelevant to the discussion about this game anyway. This is set in a future time, which is much closer in time to american slavery and its connotations than roman slavery. But this game doesn't try to emulate roman or american slavery anyway.
Just wanted to make sure no one thinks roman slavery was halfway decent. It wasn't. Any kind of slavery where anyone is considered property is despicable and people will do horrible and inhuman things to said slaves. It only works as a fantasy in games like this.