="Tubey, post: 7855794, member: 8574"
Sorry mate but this is a ridiculous rewrite of history. Slavery was socially acceptable for a very long time. You'll be able to find isolated examples of advocates throughout history but the overwhelming majority either turned a blind eye or simply didn't care. The rich simply got richer from them as a commodity.
Even the Valladolid debate you mention was 16th century and effectively the first time the notion had ever been discussed. It was the 19th century when it was abolished in England. The landscape changed gradually, but let's not pretend it was anything less than unaminous public opinion that black people were basically animals to be treated as property for hundreds of years.
In Edward Colston's era, the 17th century, his trade was seen as completely normal by society at large. That's an indisputable fact. It was very much "the done thing".