Certainly it is a utilitarian argument, but in the capitalistic sense a business (plantation) that uses slaves is less efficient in terms of net productivity of the slave than if the slaves were free and instead workers competing to improve the business.
Note: I'm not saying there is no moral reason slavery is wrong, just that in addition it is contrary to the nature of capitalism.
Note: I'm not saying there is no moral reason slavery is wrong, just that in addition it is contrary to the nature of capitalism.