I think you're conflating making someone work to pay someone back, with taking an innocent person and selling them as a slave, which I would say is what slavery is.
Agree. Exodus 22:3:
The thief shall make restitution, but if unable to do so, shall be sold for the theft.
What do you think being sold means in this context? I think it means they will be sold as a slave.
Christianity is obeying Christ. If these guys believed they were helping the slaves by paying a slaver for them, treating them well and giving them freedom after a certain time then they weren't doing anything wrong.
I would say not freeing them as soon as they could is not exactly right.
In name only, if they were hard-arsed.
Henry VIII was an exemplary Christian. The Pope commended him for it, but he was pretty hard arsed. You are perpetrating the No True Scotsman fallacy.
Which bits do you think should be taken out?
I don't go much on putting people to death for being gay or adulterers or being raped and not crying out or working on the Sabbath.
Precisely, and it was this that had to be stopped, or changed to a system of temporary work in exchange for freedom to live as free men.
Given that slaves
were transported to the Americas, it was pretty much impossible to send them back once they gained their freedom. Firstly, the Atlantic crossing would have been quite dangerous and would have killed many of them. Secondly, there were probably very few first generation slaves left at the time they achieved emancipation. It would have been an act of cruelty to send people to a different continent to the one on which they had been living their whole lives.
You also couldn't just say "hey you're free" and leave them to their own devices. That would have been pretty cruel too.
The above considerations about freeing slaves is just one aspect of why they should never have been made slaves in the first place.