I've several times now run across a new linguistic trend, mostly among a certain brand of academic. When writing about people we would normally call slaves, the new trend is to call them "enslaved people". I assume the reasoning here is because we don't want to define someone by their enslavement, as if it's an identity-forming feature of their existence, and we shouldn't let someone in one of the most oppressive situations be defined by something entirely outside their control that has demeaning connotations. In that way, it reflects some of the concerns of person-first language, which I've usually encountered in the context of disabilities.
[See my critique of person-first language. It's a bit over-the-top, as most satire is. The sense you get from it about what my views must be is not quite what they are. I'm not completely opposed to person-first language, and I even think sometimes it's the best way to go in certain settings. I would say that with small children it's far better to speak that way, whereas with older children and adults it's best to help them understand the categories we in fact use while drawing attention to the ways we illegitimately think about those categories and ways we process them unconsciously and thus denigrate the people we're talking about without always being aware of it.]
But this is different. For one thing, this isn't person-first language. Person-first language would not speak of enslaved people. It would speak of people with enslavement or people encumbered by, trapped by, oppressed by, or otherwise affected by enslavement. Person-first language is so roundabout, awkward, and unworkable that even those tempted to apply it in this case have actually refused to go that far. They will avail themselves of adjectives rather than nouns and use the adjectives to modify the noun 'people' or 'person'. It's grammatically parallel to "deaf people" or "autistic people" rather than "people without hearing" or "people with autism". But it's certainly a step in the direction of person-first language when compared with calling people slaves. The only grammatical equivalent is to speak of the deaf with no noun or to talk about people with autism as autists. [I should note that that's a bad idea even if there weren't any other problems with the term, because people will just think you're from Brooklyn or the Bronx and talking about people with very creative abilities and outlets.]
But there are differences, and I think some of them matter morally. One is that ordinary language does allow for slaves, and "enslaved people" is awkward, whereas "autistic people" or "people with autism" are both common, while "autists" is not. Another is that it's generally accepted that calling someone an autist is unacceptable, and it's at least not generally unacceptable to call someone who is enslaved a slave. That's not the only issue, but that's a difference. For example, it was much worse to call people retarded once that became a standard insult for people without any cognitive disabilities than it was when it was the accepted term and had not yet been used as an insult. Whether it was a good term ever is something people can debate, but surely it's made worse once it becomes used as an insult. So the fact that a lot of people do oppose a way of speaking does count more against it, and the fact that many people approve of a way of speaking does mean there's less to count against it, whatever else is true.
Another difference is that one is a disability and the other is an imposed condition. Both are involuntary, at least in most cases of slavery. Slavery can be accepted voluntary, especially in cases of indentured servanthood, selling oneself into slavery to pay off a debt, or accepting slavery to avoid a death penalty (well, that's at least not completely involuntary, although it's not actually a range of choices that anyone would consider sufficient for the choice to be fully voluntary). But one is known, at least by most people today, to be something that is not central to who one is but rather imposed. No one today, at least no one I personally know, thinks that anyone who is a slave is the sort of person whose slavery is necessary because they couldn't otherwise function in life. No one thinks slaved naturally deserve slavery. No one thinks it's part of a slave's nature to be a slave.
This is not true with racial categorizations. As much as we might discover scientifically about how there isn't all that much difference between different racial groups, we do process racial categories with stigmatized stereotypes, and scientific studies for decades now have consistently shown that these stereotypes and stigmatized categories will affect how we treat people, at least in small ways that most of us don't pick up on (and especially in situations where we're tired or busy and have to make decisions quickly without thinking carefully about them). This isn't true of the category "slave" even if it is true of other contingent categories. If I find out someone is a slave, I'm not going to process that the way I do if I find out they receive welfare, are homeless, or grew up in a ghetto. Whether I want to or not, I will make assumptions about the person if I discover they're in one of those other categories, and I won't if I find out someone had kidnapped and enslaved them. We're distant enough from the 19th-century practice of slavery (and what does go on today is both under the radar and officially disapproved of) that we just don't respond that way anymore.
So one of the important reasons for avoiding linguistic constructions that serve to foster innatist, essentialist thinking (which really only matters with small children anyway, according to the most careful psychological studies) does not matter with slavery. That means any argument for preferring "enslaved people" to "slaves" must have to do with how people in those categories would perceive it, not how others will be influenced by speaking or hearing the construction. And I suspect the same debate that occurs with disability would crop up here. People who prefer "person with autism" are usually parents, teachers, and psychologists who want to encourage not defining someone by the disability and who want others to respect them as people, taking their interests and desires as important, assuming competence first before assuming incompetence, and other essential features of treating someone as a person. Yet one can do that while using the word "autistic" as an adjective.
The other side is usually from people who have the condition who have the communication skills to express their view on the matter. They in fact prefer to be called "autistic" as an adjective, just as the deaf community generally prefers to be called "deaf" and thinks person-first language is insulting. Why is that? Because they see their condition (which they don't always see merely as a disability, because it involves both impairments and increased abilities) as something very important to who they are. It shouldn't define them as if it's the only thing that matters, but it is part of how they've formed their identity, just as race is for anyone who isn't in the dominant majority racial group in their social location. White people in the U.S. don't see whiteness as part of their identity, because it's part of white privilege not to be affected by race is ways that make you constantly think about those categories. Most members of other racial groups in the U.S. do consider their race to inform their sense of their own identity in significant enough ways that they wouldn't want people not to think of them according to those categories, as the dishonest color-blind ideal (does anyone really think they can pretend not to see race?) would have it.
How should this affect calling people "slaves" vs. "enslaved people"? Well, not having the chance to interview a bunch of people in that category, I just have to guess, but my suspicion is that it's going to be like race and disability, at least in terms of how they think of their identity while enslaved. It's pretty all-defining of what their life is. I can't see how that wouldn't be identity-forming. It's certainly more easily removed than the other cases I've been discussing, and that's why we can speak of people as former slaves. But that linguistic option show that we can handle the contingency of the category while still availing ourselves of the ordinary way of speaking, and there is at least some moral argument for retaining the category rather than abandoning it, which gives me little reason to want to engage in a major effort to revise our language in a pretty large way.