What has Christianity truly contributed to humanity

[Thumpalumpacus]

You must, however, from this adduce that morals change over time, as you tacitly admit here.

Or you might simply say that you support Biblical slavery and be honest about it.

You cannot, however, argue that the Bible is inerrant and argue that slavery is wrong -- unless you admit that morality is relative and/or subjective, or put shortly, not absolute.

This is the Christian conundrum, and on more issues than slavery. Morality is both relative and subjective, but you cannot acknowledge that without undermining your own god's alleged moral authority.

I do not support any kind of slavery. 

I have never argued that the Bible is inerrant. 

I do not know if morality is relative and subjective, or if it is real but that our understanding of it develops over time. 

I have never made any claims regarding any god's moral authority.

I'm sorry; I had thought you were Christian. Apologies for the error.