I’ve put a lot of thought – probably more than most people – into humanoid monsters. Anytime I consider a baddie from the prime material plane with opposable thumbs, a language, and a reasonable intelligence score, I wonder what makes that creature evil; what makes it a monster, if you will. I’ve had these sorts of philosophical thoughts about creatures like orcs and goblins since the first time a character of mine encountered a lair of such creatures that contained women and children who were the non-combatant family members of the monsters who were trying to kill us.
The most expedient way to answer the question of nature versus nurture when it comes to evil is to say that such monsters are “irredeemably evil” by nature, with no chance for even an orc left on a kindly farmer’s doorstep at birth to grow up to be anything but a pillaging, murderous monster. Answering the question in this way allows your party of murder hobos to dispatch the defenseless, infant monsters while sidestepping any issues about morality or their own personal alignments or beliefs. Essentially, this answer is “the easy way out,” and it never sat well with me.
Besides, is this answer really easy? We’ll stick with just orcs for the moment. If we say that orcs are innately and irrevocably evil, then this begs the question: “Why?” To answer this you might argue that orcs are always evil because their deity, Gruumsh, created them without free will. Sure, they could make choices, but they could never choose to do anything altruistically “good.” Because if even just one orc had the ability to make an altruistic decision then the whole argument is bogus, and killing those defenseless orc children would be murder, plain and simple.
The same thing would have to be true for all of those other evil monsters, too. And if you want that sort of black and white dichotomy of good versus evil that’s fine. But if that’s the case, why even have monster children? Maybe you don’t have them in your games (I generally don’t have them in mine). I only mention them because the old monster books mention them, and adventures from older editions of Dungeons and Dragons are filled with them. And I feel like they were put there to create a moral quandary, not just so your adventurers would have monster babies to kill. Besides, it’s possible to make a creature innately evil and eliminate the “offspring dilemma.”
Of course the opposite is also true: it’s entirely possible to have monsters that aren’t innately evil and also not deal with questions about whether or not you should slay monster children. Just don’t put monster kids in your adventures. This is pretty much what I do with most monstrous humanoids. Taking the “not innately evil” approach allows you to do other cool things with your monsters, like have fantasy cities with taverns that bear a resemblance to the Mos Eisley cantina. Because if there are members of a race that aren’t evil, it stands to reason that you could find some of those creatures mingling with the other civilized races of the world.
This approach also makes you think of these monsters, and their place in your world, in a more holistic way. Perhaps these monsters even have their own kingdoms. Such a kingdom and society could still be dominated by lawful evil ideals and practices, such as despotism and slavery. But allowing for exceptions to these rules opens up the possibility for much richer interactions within the game world. Perhaps there is a hobgoblin kingdom on the border of civilization that is largely shunned but whose mercenary companies are highly sought after by lords who can afford them because of their unwavering loyalty (once they’ve been paid), and their willingness to do unscrupulous things. Maybe the king of a realm which borders a sizable swamp has an uneasy but long-standing trade agreement with the lizardmen who reside in said swamp, perhaps trading metal tools for peat moss and salt from the marshes. Maybe the local inn keeper has an ogre bouncer that lives in a well-appointed cave on the edge of town and who is treated as an equal by all of the villagers.
Obviously I’m not saying that every orc you run into needs to be an aspiring paladin or that every hill giant has a heart of gold. I’m just saying that a world in which these things are possible is a more interesting world than the alternative.