Why was violence the default reaction to slaves? Were any slave owners kind (yes, I know owning slaves in itself isn't "kind")? Is there evidence to suggest kinder owners had better production than violent owners or vice versa?
There is no such thing as 'fair' slavery. African American slaves were human beings treated, bought and sold as property.
/u/Freedmenspatrol and /u/Sowser have discussed the concept of 'nice' slave-ownership in great detail in their respective pieces:
Whilst slavery was happening in the US, how common was it for families to treat their slaves very well? /u/Freedmenspatrol
Suffering slaves and suffering serfs, whats the diff? - /u/sowser