Viewing slavery as a moral or economic issue makes it easier to talk about, since it removes people from the conversation, allowing opportunities for compromise, ways to get along, ways to talk past the difficult conccept of people being used. That was often how such discussions of slavery in the Uniited States had gone for a while.

Harriet Beecheer Stowe's story of enslaved people in the South moved the conversation in a less comfortable direction, by making the suffering of slaves personal and specific.

https://en.wikipedia.org/wiki/Uncle_Tom%27s_Cabin

https://en.wikipedia.org/wiki/Solomon_Northup

https://en.wikipedia.org/wiki/Frederick_Douglass

https://en.wikipedia.org/wiki/Narrative_of_the_Life_of_Frederick_Douglass,_an_American_Slave