The problem with putting everyone without rights in the slave category is that it is not how we commonly or historically use the word 'slave'. It isn't even the technical meaning of the word 'slave'. A slave is someone that does forced labour of which he cannot choose to leave for some other labour (note that being a slave is not being forced to Have work, lest you make the word completely useless because that would make every single thing in the universe a slave in some capacity; it is specifically the instance of the person in question being forced by external forces to specific tasks). This presumes passivity. In the sense that you are not a slave until you accept your slavery to some degree (if you fight to the death when someone tries to capture you, you were never enslaved. It takes actually being captured or submitting to work to actually be a de facto slave). Human beings are autonomous creatures. We choose our actions. If I have no rights under the law that does not automatically make me a slave because that presupposes that I will go along with it. Which I can choose not to. The natural state of this individual is simply that of Outlaw. Of being outside of the law and thus without any guarentees. That means I CAN be enslaved. But I can also Not be enslaved. A man can be completely outside the law and live a normal life if nobody decides to force them to do something. It is this act of submitting to someone that is actively forcing them into service that constitutes their slavery.
Your definition of slave as simply someone that is forced to do specific work by external compulsion does not work for reasons already mentioned, plenty of people throughout history that were not slaves have been forced to do work. Take for instance conscripts in a war, they are not slaves but they are still compelled by the government to work as soldiers fighting their war. Forced labour while a necessary element of slavery is not a sufficient condition, the other condition is that the slaves are property with economic value and/or the slaves products have an economic value. To conscript your own people to fight a war is not slavery, but to conscript people to form a mercenary company that is hired by another party *is* slavery.
The rest of what you are saying has echoes of
Kayne West's slaves choosing to be slaves. Slavery is not a choice made by the individual slave, slavery is a choice made by society over the head of the slave and the slave has no choice but to be part of the society in which they are a slave, because
free people also have no choice but to be part of a society. Under the Slavery-By-Default model, an Outlaw is very much similar to a slave, a Slave is what the Outlaw becomes if the Outlaw becomes part of a group but does not lose that status; conversely an outlaw is a slave that nobody owns (yet).
Human beings are supposed to be social creatures, so an outlaw hiding from everyone in the wilderness is not living a normal life. In fact the prospect of such a fate is nasty enough to most human beings to constitute a coercive mechanism to get people to do/not do things; in fact outlawing was an mechanism *of* the Anglosaxon law to punish particularly nasty criminals. If I choose to accept the punishment rather than comply, this does not mean I am not being coerced; as the option to accept to be punished is simply the other side of the coin to compliance in any coercive system; you cannot choose not to be coerced unless you can evade the punishment.
When both death and exile/ostracism into the wilderness are both punishments, slaves cannot choose to *not* be coerced since there is no option of evasion that exists here. That I have a choice between a varying set of nasty punishments for not complying does not make my complying in any way voluntary.
Also I like your Slave-by-default approach but again I wouldn't call it slave-by-default but Outlaw-by-default, in the sense that a person CAN kill and/or enslave you (an action, not something that you are by default because you could resist it and won't necessarily start obaying your random Citizen Joe just because he orders you to do something and you aren't a citizen there). This is a nice way of doing things because that opens the door for Treaties between civs to protect their citizens from abuse or even to permit civs to create such protections spontaneously depending on their ethics or population concentration (ancient peoples many times created seperate law codes for different groups of foreigners in their territories. An extensive example of that is the ancient roman leges barbarorum or the mesopotamian laws regarding the gigantic variety of peoples living there)
This.
As for implementing slavery properly?
I think the game should move over to the proper, common usage of the word 'caste' and implement civ-level castes or "strata" if you've played Stellaris recently. "Status" works too. The word doesn't matter, what matters is a functional simulation of social hierarchy. Seriously, there is no single greater feature that this game lacks
I am quite the Stellaris fan and I know what you are talking about. I also play with Shared Burdens so all social strata are equal anyway for my civilization.
Really the game does quite fine without social statuses, it seems to presently demonstrate their redundancy.
The problem is fortress mode not adventure. While if we are only one dwarf fortress controlled by a central government and there are many other fortresses, you could find yourself in a position of having to play along with the societies oppressive institutions because of laws/external regulation, but as the last surviving fortress and with the king as a member of your fortress, then there is no logic to why we would respect oppressive social orders at all.
The problem here is player freedom. If the social distinctions being made are pointless and irrational, the player will only respect them if they are forced to do so by the game mechanics while if they are made purposeful and rational, the game is basically politically advocating *for* such a system. In adventure mode this is no problem, you are only an individual/small group and having to live in a society that does not agree with you or make sense entirely is quite realistic. When we are talking fortress mode however, we have the problem where we can really have enough political power to abolish slavery and any oppressive institution we do not like.