As an atheist, i don't believe in souls, however i still think you argument holds value. Perhaps not a soul, but if the robot is capable of sentient thought on par with humans, including emotions, reasoning, compassion, etc., i feel it deserves the same rights we all have, is free will not the defining characteristic of a sentient lifeform/robot? is a robot possessing free will any less deserving of life than a human, simply because it is a metal construct?
I don't know if this is off topic, but i think it ties in somehow