We traded with the Brazen Throne, who are way worse than the Opaline Vault, we will trade with the Opaline Vault gladly, and we will take mercenary contracts against the Brazen Throne from them as well, because taking down the Brazen Throne, is way higher priority than ending slavery in the Opaline Vault, if we ever become stronger than the Opaline Vault, then we can begin to use political pressure to have them stop using slavery, but we will probably never outright go to war against them, not because we don't believe their form of slavery is wrong, but because their slavery is benignt enough, that there's thousands of policies, that are the greater evil compared to the Opaline Vault.
We will trade with anyone we aren't currently actively at war with, trading with them however, don't mean we wont conquer or kill them in the future, it just mean they have things we want, and we currently can't afford to take them by force.
Our trade fleet trade with the Free cities, that don't mean we don't plan to conquer them in the next decade, all policies that practice slavery or other such vile practices, are on the list of places to be conquered, if we can't talk them into changing voluntarily.
The Opaline Vault is technically on the list too, but it's very much technically, because there's so many higher priority targets on the list, so for now we occasionally work for the Opaline Vault, because they pay well, and their contracts pit us against people far higher on the list than the Opaline Vault are.