I would be terrified by a machine that took those kind of decisions over human life without taking into consideration the specifics of each particular situation

I would be terrified by a machine that took those kind of decisions over human life without taking into consideration the specifics of each particular situation, merely from an abstract rule that some engineers thought of and derived from first principles in their laboratory, without input from the real world or from a limited sample of cases. In your hypothetical example, what if the elder was the only leader of a faction that could negotiate a tready and avoid a global war, but the robot has no built-in rules to detect such development and kills the elder anyway? There's a reason why we keep judges around to interpret and implement the law, even if the rules are established by an independent body and are in theory are designed to maximize the common good. The moral of Asimov stories was that it is impossible to encode morality as a simple set of rules, as the complexity of real life will always produce unpredictable situations, and ethics will provide ambiguous answers depending on which principles are considered more important.