That’s an interesting question you pose. The first thing I want to do in response is chew the concepts of liberty and good a bit. What follows will be from a broadly Objectivist perspective, because I’m broadly Objectivist in my outlook on this issue.
From the Objectivist point of view, something is good if it supports or contributes to the survival and flourishing of an individual organism. Something is evil if it frustrates, damages or undermines the organism’s survival and flourishing.
Liberty is the political condition of being free from the initiation of physical force. For liberty to be good for some organism, it has to be the case that being free from force contributes to that organism’s survival and flourishing. Or, putting the point the opposite way, it has to be the case that being subjected to force damages the organism’s ability to survive and flourish.
Why is liberty important for human beings? Because the fundamental tool of human survival and flourishing is the mind, and the mind cannot operate under force. Force creates a breach between my understanding of the world and my ability to act. This breach destroys my ability to use my best life-supporting capacity, and thus undermines my survival and flourishing.
So with respect to hypothetical aliens, the question of whether liberty is a value to them largely reduces to the question of whether using force against them damages their ability to survive and flourish.
With respect specifically to the issue of free will, it seems obvious to me that aliens who lack free will do not face the question of how they should organize their society (because they have no choice in the matter); our treatment of such aliens should be driven by the requirements of our own survival and flourishing.
