i) From a secular standpoint, Tony needs to explain why owning slaves is morally wrong:

a) To begin with, many secular thinkers admit that atheism leads to moral relativism or moral nihilism.

b) In addition, secularism has a very reductionist view of humans. We're just animals. Temporary, fortuitous organizations of matter. So even if an atheist could get over the first hurdle (are there objective moral norms?), why is it wrong to enslave a human animal?

ii) The fact that Biblical law regulates slavery doesn't necessarily mean the Bible condones slavery. Law codes aren't ethical ideals. They simply set a floor for social mores. A minimal standard for what's socially intolerable. The law is not a substitute for moral and spiritual renewal.

iii) There were basically two reasons for "slavery" in the OT. One was for captured enemy combatants. Well, what's the alternative? If you defeat the enemy on the battlefield today, but let the defeated soldiers go home, you have to keep fighting the same battle. So that leaves you with two practical alternatives: (a) execute them or (b) subjugate them.

iv) The other reason was insolvency. Indentured service is no fun, but it's preferable to starvation.

v) As Richard Bauckham discusses in The Climax of Prophecy, Rev 18 is a searing indictment of an economy based on forced labor.