My reference to the US experience was not intended to indicate that I was only speaking of slavery as practiced in the US.
My point was that slavery as an institution (irrespective of the particular form practiced in one country in recent centuries) goes back as far as recorded history: a fact that was repeatedly referenced by anti-abolitionists. They pointed out, quite correctly, that many of the great and noble civilisations of the past had rested on slave labour, and concluded from this that (a) slavery is a civilised and enlightened institution, and (b) civilisation could not survive if it were abolished. History has not supported either conclusion.
I think I may reasonably draw a parallel with other cultural norms of equal antiquity which are now called into question, and which some claim to be (a) civilised and enlightened, and (b) essential to the health of society.