Slavery - Torah vs 1850 Fugitive Slave Laws

Torah clearly states in many places that the 'slave' must be treated well.

In Dueteronomy 23:16-17 it says you should not return the slave who seeks refuge with you and that you should treat the slave well.

Link: Gary Charlestein reviews laws about slavery in Torah

And yet in the 1850's in the south of the US the slave laws prohibited 'harboring slaves' with very severe penalties. This law was anulled in 1862 but these laws were clearly in conflict with Torah laws.