Lots of crickets on this one. It's a tough subject.

A couple of thoughts.
First, note that there is no such thing as ethnic slavery. It's foreign to the times. In fact, to my knowledge, it was a fairly new development when the Muslims began "stealing" Europeans in order to enslave them. This is where we get the term, referring to Slavs that were enslaved.
Second, the OT directly condemns man-stealing. Nobody could be enslaved just because they were caught.
Third, if we look at the passages dealing with slavery in the OT, we'll see that there are aspects of each one that in some form, at least, protects those being enslaved. For instance, rather than destroying those who surrendered, they were enslaved. And slaves, in ancient Israel, enjoyed some protection. They were not to be beaten or treated poorly. They were to be more like members of the family, in some ways, or at least hired servants.
I have often wondered if a more just form of "punishment" for true crimes should be some sort of servitude in which the aggressor must make amends to the victim. Right now they serve time and get fined, often with the state reaping the benefits while their cronies in the prison system continue to profit. It's a rigged game with no real focus on compensating the real victims. We won't even get into the extortion of victimless crimes.
So how about if someone kills a husband/father, it becomes their burden to provide for that family for the rest of their lives? Out of every dollar they make from that point on, they must pay 50 cents to the family. There is no reprieve, if they're guilty. And the true victim receives some form of compensation for their loss. It can't ever be perfect, but at least the culprit is forced to make some amends to the victim. And the state isn't in a position to profit from the criminal system.
This would be a form of slavery, in some ways. But it seems just and certain is far better than throwing them in prison where all they do is make private prison owners wealthy off funds extorted from the public. It also falls in line with much of the teaching of the OT.