apparently not having any issue with the idea of one person owning another as property?
That condition is effectively just what Paul opposed: he told masters that slaves were
not their property, with whom they could do as they wished:
'Masters, treat your slaves in the same way. Do not threaten them, since you know that he who is both their Master and yours is in heaven, and there is no favouritism with him.' Eph 6:9 NIV
'Masters, provide your slaves with what is right and fair, because you know that you also have a Master in heaven.' Col 4:1 NIV
In effect, the master-slave relationship became triangular in the Christian household, with deity providing the controlling factor among people who were better related than ordinary brothers and sisters. In effect, Christianity tended to subvert slavery, by showing the human relationship upon which the practice depended to be a false, unnatural and indeed inhumane one- no matter what any apostle wrote. There must have been many slaves and masters who were the greatest personal friends, treating each other as equals, in private, but going through the motions of the slave relationship in public. It's not too surprising if the Roman Empire disapproved of a 'leveller' faith, which of course it famously did. Had it not done so, had Christianity been allowed to survive and flourish, one can be reasonably certain that slavery would not have survived.
On a wider, socio-political level, one must be practical about this. Paul was in no position to change the economic basis of what is euphemistically called classical civilisation- at least, not directly. Had everyone become Christian (and Paul considered that all were commanded to do so), slaves would surely have become a thing of the past. Had Christians, in a minority, given up their slaves, they would have been at severe economic disadvantage. And of course, none of the apostles was prepared to make a slave revolt part of the manifesto, because it was useless to gain physical freedom, but go to hell afterwards. The gospel was their overriding concern, as Paul repeatedly pointed out, and that should be the factor constantly borne in mind by modern commentators.