I am not sure your analogy is correct with regard to the lack of free will and Giaks. You're basically describing a creature having free will and being labelled as different despite no other difference in behaviour from a real person. Let's say your zombie is like a human in everyway but, being possessed by the will of the Evil God of Youth, enters a frenzy and MUST kill anyone above 60 years old he sees. There is no way to prevent him entering that state, and he'll explain, outside of these rages, that it is perfectly normal to kill people elderlies because they are abominations. At this point, he has already dismembered three people in the street, but he's otherwise a very fine fellow when conversing with up-to-59 years old. What would you do with that zombie, knowing that there is no way to rehabilitate him ever to be able for him to live within a human town? Outside of making him in charge of balancing the funding of the pension system, of course.
[Example from Magnamund "always evil" denizens of Helgedad: if you unsheathe the Sommerswerd within the confine of the city, all its inhabitants -- otherwise sentient -- will converge toward you lemming-like to kill you even if it means dying en masse. Your quest, and your life, ends here.]
Though there is a case to be made following your line of thought, I've also find that it's not really conclusive to a hobby where most of the time, killing people is the general (even memetic) behaviour of adventurers, since it would result in even, say, killing devils and demons not being justified.