I'll join you on the limb and say that the Old Testament never uses the word 'slave'.
If you buy and sell people, they are slaves. You can call them 'servants', you can call them 'chattel', you can call them chinchillas if it makes you happy, but they're slaves.
You could buy or sell a servant, but you had the same master as him/her which was God.
Which just suggests that one of the reasons God doesn't speak out about the abhorrence of the practice is that he partakes of it.
So, according to the NT, just as wives are told to submit to their husbands and husbands to love their wives and give themselves for them, servants are to obey their masters and masters are not to threaten their servants, Ephesians 6:5,9. However, both these ideals have been abused over millennia, and so today the first is taboo and the second is illegal, in order to prevent abuse.
The idea of women having to submit to their male relatives is not 'an ideal'. The only way to enforce slavery is through the threat of violence - even God maintains his slaves with the threat of an eternity of torment.
Drugs are illegal because they are abused, but can be good if used in the right way, eg antidepressants for someone who can't produce the chemicals in their brain.
Some drugs are illegal (i.e. heroin). Some are tightly controlled (i.e. most medications). Some are loosely controlled (i.e. aspirin) . Some are freely available (i.e. coffee). Within those categories are some that are illegal, ostensibly because they are horrendously harmful, but without any strong evidence to support that claim (i.e. marijuana), whilst others are loosely controlled but demonstrably cause great harm to society and the people within it (i.e. alcohol, tobacco). Drugs are not illegal because they are abused, necessarily, drugs are ostensibly controlled because they are potentially harmful, and to an extent dependent upon the ease and extent of that harm.
I can't see a problem with someone who has nothing becoming a servant to someone who can give him food and a roof over his head. That person has saved his life, so in a sense he owes him his life, but that doesn't make him a slave!
But him being a commodity that can be sold does. Working for your keep is not, intrinsically, a moral problem, even if you barely get a subsistence living - it might not be in keeping with the concepts of Christian charity or our more modern sensibilities around a living wage and a suitable work-lift balance, but it's not a categoric evil. Owning people is.
So I'll go further out on the limb and say that the word 'slave' by default implies mistreatment, as well as being owned.
Nope, just the ownership bit. A well treated slave is still a slave, because you can still decide that you've had enough of them and that you're going to sell them to Bob down the road and they don't have a say in that because they're property and your rights over them supersede theirs.
O.