I don't believe in the original sin of slavery in Western countries.
Slavery has been existed for centuries before and, despite being abolished by Western countries (hint: there were several wars were people lost lives), still exists in China, India, Indonesia, and a large group of Arab countries.
> I don't believe in the original sin of slavery in Western countries.
I have no idea what that sentence is specifically meant to mean, that aside, western countries have had actual slavery and effective slavery both in the past and the present.
I don't mean to exclusively beat on Christians or just Catholics here; but I do intend to counter your apparent narrative of good Christians and evil Muslims.
Christians certainly diminished a lot of cultures, just as other religions also did - the initial point that started this above.
There has never been as many slaves in humanity as there are in the US' prisons.
What's that? Oh, they don't count because they're criminals?