You probably want to start here – my “Ethics of Pokémon Training” is by a fair margin the most popular thing I’ve ever written. I essentially try to argue here that the act of catching a Pokémon represents a sort of ritualised contract that is made between a Pokémon and a trainer, and that this contract can be broken by either party. You can also read this, where I compare Pokémon to professional gladiators and Greek teachers and doctors under the Roman Empire, who were technically slaves but in some cases got a pretty good deal out of it. See also here, here and here.
So, the thing is, if we take a very bland and clinical definition of slavery – ownership of one sapient being by another – then Pokémon sort of are slaves (or at the very least indentured, bound to their trainers for a specific purpose). You can’t really get around that. I happen to think it’s unhelpful to talk about them in those terms, because slavery is such a loaded concept in the real world, particularly for Americans, what with their role in the Atlantic slave trade, their civil war, and its continuing impact on politics and race relations in the country. Most historical instances of slavery were pretty damn terrible, but you do get a few specific, anomalous cases in civilisations like the Roman Empire or ancient China, where some people who are technically slaves are able to seek advancement and do well for themselves anyway. This is more or less how I would characterise Pokémon – they’re technically slaves, but it works because there’s a vast and complicated framework of cultural, legal and ideological traditions in place, something the real world could never imitate, that exists to protect their rights and prevent the kind of abuses that normally go hand in hand with slavery. People like Team Rocket exist, but are the exception rather than the rule.
Of course, once we say all of that, we then come perilously close to retreading the arguments that were actually used historically as justifications for slavery, because in societies that practice slavery it’s quite common to believe that the slaves are better off, that they are in some way not suited for freedom. And this is why it’s really important to have stories like Black and White that actually try to grapple with this, and really important to have characters like N who express doubts about the whole thing (by the end of Black and White 2, he’s convinced that it’s good for humans and Pokémon to be together, but still has doubts about how that relationship works in practice, and particularly about the use of Pokéballs). There are dubious elements to the whole thing, there is terrible potential for abuse (because, again, Team Rocket exists!), and it’s when Pokémon stops trying to dodge the question and instead just engages it, grabs the bull by the horns, that it tells its best and most interesting stories.
It’s complicated, and maybe I should address it at length again in another article…