It was an interesting listen but flawed for several reasons. The human kingdom has no standing army as stated in the light novels, they are all conscripted and only called up when something vast threatens the kingdom. Goblins are the weakest monster around. Their urge to rape and torture is most likely driven by high testosterone so castration would make them dull and lethargic is my guess. Not to mention there are clear lines of ethics in that world and this would turn the kingdom on its head. And the most glaring oversight of the ENTIRE video is that now you have a dedicated terrorist blowing up state run goblin facilities with ruthless efficiency.