Okay, then we shouldn't be talking about imaginary laws that the Jews had to follow that you have no evidence for existing.
Where does the NT refer to slaves then? Not to bondservants, but to slaves.
If the Bible doesn't mention something, then the Bible ignored it. Maybe Christianity didn't ignore it, but the Bible did. So where is this "common knowledge"? It wasn't common knowledge amongst Romans or Jews that slavery was wrong, so it had to be a new idea that came along with Christianity. Where is your reference that slavery being wrong was common knowledge amongst Christians?
You argument is circular. Because the masters were Christians, they wouldn't own slaves, because Christians don't own slaves, and that's how you know they weren't supposed to. Why did the Christian masters know they weren't supposed to own slaves?
You said that it is because Romans controlled commerce that we know they didn't allow Jews to buy slaves. That is non-sequitur. There is nothing special about slavery in that statement. We could apply that logic to any product that Jews wanted to purchase. If you want to claim that Jews weren't allowed to purchase slaves, you need to show me a reference to a Roman law that says they couldn't or a reference to a Jew talking about a such a restriction. Otherwise it is imagined.
I can see you are putting quite an effort into proving the immorality of certain cultural aspects of 3500-year-old civilizations, not to mention that Paul seemed to be focused on personal relationships rather than hot-button issues of our day such as equality.
But why think the Bible is reducible to a moral code?
Given that it claims to be both Divine and Human in origin, why think authors didn't have freedom to represent their prescientific view of science, or premedical view of medicine, or that in a world where ever culture had slaves that the ancient Israelites would limit the abuses of slavery and maximize the benefits (safety, food, shelter, for the poor and dispossessed)?
By misrepresenting the point of the collection of books as a moral code, you created a straw man.
Secondly, you are quibbling over word usage when you could have pointed out that tradition has it that the Torah was written by a murderer (Moses), and a good portion of Psalms was written by a murderer (David), and a good portion of the New Testament was written by an accomplice to murder (Paul, chased down many Christian leaders, and imprisoned them, some of which were stoned to death).
When ever you transport a modern view back into history as a way to judge that culture, you have committed the fallacy of anachronism.
Clearly the Bible is written, not as a moral code but as a variety of experiences having to do with God or his people written by over 40 authors, from Kings to outlaws, criminals to heroes, the poorest to the richest, spanning 1500+ years.
You can get Christians to argue due to their lack of knowledge about your particular fallacies or intuition about your rhetorical strategies, sure. But why not ask Christians questions that would anchor your premises?
1. What is the nature of the Bible?
2. How is it different that other religious books?
3. What is the nature of "The Law," as recorded in the OT?
4. Is that Law a universal moral code?
5. Why did the authors of the Old and New Testaments only interact mildly about great social injustices? (This may not be the case)
6. Why did Christians creat the first:
Elder hostiles
Orphanages
Hospitals
Shelters for the poor
If their scriptures didn't even provide freedom for slavery?
7. Why did the Jews treat foreigners, widows, orphans, poor, infirm so much better than all their neighboring cultures?
If in fact one is a "seeker," one would expect questions about the nature of the thing one is seeking, rather than strawman constructions popular to individuals's go are clearly not seeking (New Atheists).
Seekers don't defend fallacious propaganda. Propagandist do.
The New Atheist never tire, but "seekers" learn and change their arguments into sound ones.