There are at least half a dozen passages in the New Testament supporting slavery. At worst, it seems like a bad idea to go out and capture slaves, but there's no problem owning them.
Again from history, the Roman slavery was an indentured servitude kind of thing. Instead of debtors' prisons, they had this. Palestine was under Roman rule and there were a lot of things in Old Testament law that the Romans did not allow them to do (just like we aren't allowing stonings in Iraq today). Had they been able to, Jesus wouldn't have been crucified, but stoned.