You cannot separate the morality of an action from it's usefulness to business, thats putting the horse before the cart.

Modifying your last sentence illustrates this nicely:

You can argue that slavery is a net negative for the world or that it's evil or whatever you want, but if you frame it as "how can we take steps to make things better for slaves without completely destroying the way business on the world make money" then I think the current path is a reasonable one.