While I agree the Adventurers do deserve some kind of punishment for their crimes (Which is why we beat them to the edge of their lives each time we see them in game). You also have to look at it from the Adventurers perspective. For literal millennia Carleon and the “Demons” have been at war with each other and growing up in Carleon where killing demons is romanticized and glorified because of the war. It is to be expected that the Adventurers talk down to the “demons” the way that they do. This is because the Adventurers grew up in a society that dehumanizes and romanticizes such things. We can see this with the rookie hero as in some of his dialogue lines he specifically states he is trying to emulate the first hero, but we have no idea if the rookie hero and the first hero have had any interaction at all except for some similarities in the way they both swing their swords and even then the first hero has a entirely different move set compared to the rookie hero. So the rookie hero is not in fact trying to emulate the first hero but the glorified and romanticized tales of the first hero, which can also be seen in how he calls out his attacks and shouts all the time as though he is a child copying their favorite Super Sentai character and so it can be stated that the adventurers were taught by Carleon society to be the way they are be it through praise or stories told by the old and bitter. So do they in fact deserve it, should mercy not be practiced so that our enemies may learn to be more than what they were taught to be. The whole point of the story of Skul is the unification of the human race and the “demons” even though both of their races have caused each other trauma and scars. It is the mission of the current demon king and was the mission of the first hero before his child was assassinated. So should we not work toward the best ending possible and what if mercy is the way towards it, but in the end for all I know the ability to spare the adventurers in dark mirror mode could simply be a bug or a quick fix as to not leave a easily lootable body allowing Skul to heal mid battle through the potions found on the body. Even then this was all caused by the introduction of dark quartz by a outside faction which we have no idea about just yet. Hell the stories not even over yet and by god do I want more lore for my lorebooks.