So the AI provided factual information and they did not like that because 'slavery bad, therefore there was no benefit to it.' There were benefits to slavery, mainly for the owners. US had a huge cotton export at one point, with the fields being worked by slaves.

But also a very few slaves did benefit, like being able to work a job that taught them very useful skills, which let them buy their own freedom, as they were able to earn money from it. Of course being a slave in the first place would be far better, but when you are one already, learning a skill that makes you earn your freedom and get a job afterwards is quite the blessing. Plus for a few individuals it might've been living in such terrible conditions, that being forced to work while getting fed might've not been so bad...