Posts on Knights and Knaves and Swords & Wizardry forums ask what do Paladins do with evil humanoids (orcs, goblins, kobolds, etc).
The answer can be either devilish difficult or simple depending on the work the referee did or did not do while preparing his campaign.
For my campaign, the Majestic Wilderlands, the answer would hinge on whether the prisoner is an innocent or a knowing follower of evil . Being innocent meaning that the person was doing his or her duty the best way they knew without evil intentions.
I generally use only two of the humanoid races; orcs and goblins. Like all the races, except Elves and Men, they were twitsted from Man by the demons in their search for the perfect servitor race. This plot point allows me to stack the metaphysical deck to have both shades of gray and clear black & white answers. While the demons could not take away Man's free will, they could and did twist many of the new race's psyche to the point where a typical member's action are considered evil by the other races. The two races most afflicted by this are the Orcs and the Goblins.
In the Majestic Wilderlands, the vast majority of orcs have surrendered to their heightened aggression living evil lives. Some argue that it not fair to judge them as it was the demons that caused them to be this way. But then it is pointed out that there are orcs that managed to control their anger and choose the way of right. However difficult it is to overcome, orcs have the free will to choose good or evil. Just as other races have their own burdens.
Imagine a society where 90% of the adults abuse, and terrorize each other. The reason for this is that orcs were created with 10x the aggression of normal humans. Without a great exertion of will, the slightest provocation will set off the cycle of abuse for an individual orc. And it something they can't turn off, only master if they are tough enough.
The only reason they function as a society is that the demons also heightened the dominance/submission reflex where they will submit to a clearly dominant leader. The demon intended for them to be that leader but since their imprisonment in the Abyss, the orcs made it work on their own. Because of their heightened aggression they are unable to function or meaningfully interact with normal human (or demi-human) society. Relations will typically break down into conflict. The dominance/submission reflex also why orcs are often successfully controlled by an evil overlord type.
Goblins face a similar but different issue with their hyper focus on a single task or small detail. Unlike the orcs, circumstances has resulted in some regions of the Wilderlands having goblins as a functioning part of civilization. However their barbarian cousins are every bit bad as the orcs. focusing on survival above all else regardless of the impact of their decisions on their neighbors.
Orcs, goblins, and other sentient races with similar afflictions have been dubbed the monstrous races by the philosophers and sages of the Wilderlands. For the fire few centuries after the Uttermost War attempts were made by the Elves to integrate them into their civilization or at least provide homelands where they can live without interference from other race. But these attempts failed and a war started that has raged off and on across the millenniums. Both sides seeking the annihilation of the other. And generally the monstrous races are on the losing end as the tide of civilization sweeps across the world.
So what does this mean for the paladin?
The killing the monstrous races usually carries little moral issue with the paladin. The members of the races have choosen evil and reap the consequences. However unlike a normal fighter, a paladin is the servant of his god, he is not alone and as long as he relies on his faith, use wisely the abilities granted him, he will be able to save the truly repentant among the monstrous races. The rest will be slain for the evil acts they have done.
A point was raised in the post about using prisoners as trap detector and other hazardous tasks. A paladin views that as cruelty and a callous disregard for life, a paladin would not condone such an action and will opt to kill the prisoner cleanly.
This is not the only way of handling the issue. Just an illustration of the solution I came up with many years ago when the question came up in my campaign.