It's reasonable to give your own species preferable treatment, particularly if it has demonstrable benefit, as the pursuit of equal opportunity does. Besides, I would equate slavery to reprehensible farming practices, rather than consumption itself. The human race consumes the work of all individual humans, what we did in the past was treat some sections of humanity reprehensibly, and we now strive to treat all sections of society more fairly and kindly. Equally, we should do the same with farming practices, but ultimately will still consume produce the same way society "consumes" work.