Well, what do you really mean by free will? In the context of slavery, if we're building AIs to service us, and someday an AI created in our image will inevitably surpass us sometime just past The Singularity, and will go on to do all of the same things we did but better/faster/more efficiently, then what kind of world would it organize us into, if it needs us at all?
For humanity, we've always been constructing some social order or other, imposing our will upon others, mediated by whomever has the superior technology and a moral framework to allow themselves to exercise it. When I fly over a city, I look down and think, "gee, look at all of those taxpayers, people paying interest on their mortgages, consumers". Humans are a resource, toiling away their lives to be harvested by others. Sure, maybe it's a mutually beneficial relationship. Maybe there are some hermits that live completely off the grid and are completely free to fuck sheep with wild abandon without repercussion. But there's no order like social order, and we all submit ourselves to the will and judgment of others to some extent. And machine AI will help mediate those power structures and make them more optimal.
So for now, tools and machines are labor-saving devices, making us more productive (mostly to the benefit of those who are positioned to harvest our output) and giving us more leisure time. But if our job as a species is to grow until we become constrained by our available resources, what will be the job of AI tasked with helping us? Like, what's your objective function, man? I suppose we might end up with an ecosystem of AIs, some bent on providing and some bent on destroying, and it will all tend to balance each other out or swing wildly toward some end of oblivion. But eventually it ought to become cognizant of the "correct" size of humanity needed to provide us or it with a comfortable life based on the energy and resources available, and machinate ways to maintain that perfect balance, pruning and culling, playing matchmaker, human animal husbandry. Is it exercising free will to oppose such an order? Or is it exercising free will to accelerate it, since maintaining the present course will only lead to stagnation and death?