Why Do We Think Slavery is Evil?

[Angrboda]

The greatest good for the most people results when people are given the maximum freedom consistent with an ordered society.  Slavery denies this freedom to a significant proportion of the populace and thus results in less than the greatest good for the most number of people.  Is this an argument that appeals to emotion?  Certainly.  Is it an illicit or fallacious appeal to emotion?  No.

Then I would believe that a maximum amount of freedom would be a very hard bar to set. Its possible to be a slave and also have a measure of freedom. Again, I think back on the biblical accounts of slavery. For one, with Hebrews did voluntarily enter into this agreement. So they didn't feel like it was a morally improper thing in of its own to have or be a slave. And two, I don't think that they were checking out flights on Kayak.com hoping to get away to Boca for the weekend. Slaves or not, they didn't have much free time to roam about. So what freedoms were they denied?

I think you're just arguing for the heck of it, but whatever.  You're conflating all levels of freedom as being equivalent.

...[A]bolitionists attacked the economic benefits of slavery. They reasoned that the slave’s only incentive to work was out of fear for his master. Stowe illustrated this in the plantation of Simon Legree – a plantation ruled solely by fear. Slaves could not skimp on the cotton they placed in their baskets or they would face a fierce flogging. She contrasted this with St. Clare’s household where the slaves were generally left alone. St. Clare admitted that his slaves were like spoiled children, but commented that “whipping and abuse are like laudanum; you have to double the dose as the sensibilities decline” which ultimately led to a dehumanizing of slave and master. Indeed, George was one of the only slaves who did not work out of fear when he labored in a factory. But this was mainly because he was one of the most educated and desired to work to gain his freedom. Thus, Stowe contended that the African will only be the most industrious if he is educated, but such education will ultimately lead to the African seeking his freedom. Consequently, the slaveholder must keep the African debased and in fear in order to continue to enslave him.

Five Arguments Against Slavery