So, to say you like slavery implies you have some justification for it as an instrumental value.

Well, let's ask some folks who actually did like slavery, and fought for it.

From the Texas Declaration of Secession, adopted February 2, 1861:

[T]he servitude of the African race, as existing in these States, is mutually beneficial to both bond and free, and is abundantly authorized and justified by the experience of mankind, and the revealed will of the Almighty Creator, as recognized by all Christian nations [...]

So at least some people who strongly believed that slavery was moral, claimed to hold this belief on the basis of (what they believed to be) both consequential and divine-command morality.