first off, the mangaka is pretty brave to broach this kind of story. it's good because there's plenty to think about and consider past the initial shock.
second, this situation isn't cut and dried, there are several reasons why the lord's decision makes sense though they are hardly being diplomatic about it. euthanasia is a consideration for people/animals that are nearing death. being alive just for the sake of living doesn't outweigh possible pain, suffering and poor conditions that a person/animal would have to endure. if we consider the spirit's quality of life, it may make sense to end it's pain instead of keeping it alive at any cost.
a lord, at least a proper one, will always seek to bring prosperity to their subjects, and also learn from the past to avoid situations in which their people suffer. we already have the reason why the lord is desperate to use alpi who just coincidentally came: the people already suffered the destruction of one town due to not having a soul sender on hand when the last spirit died. it does not make sense that a lord would invite a past mistake to revisit their people. of course, i am not making the assumption that there are no other less sensible motivations pressing the lord, but there is a good reason to not let alpi's appearance go to waste.
i feel like they will expand on this and i hope that they will avoid simplistic caricatures