Unfortunately, it’s a Catch-22. In order to improve self-confidence, you need to practice. But it’s hard to practice without self-confidence. It might be the one skill I have to trick/berate myself into improving.

Facts
The best argument apologists have is the cultural/economic argument. Ancient Israel could not survive without slavery. But then, why couldn’t god intercede to balance their economy? Does that make god a moral relativist? What biblical morals are relative vs objective? It’s impossible to know