Okay, some background. In my campaign setting (hereafter referred to as "Duemerus", after the kingdom in which it primarily takes place), there are three main ethnicities or tribes of orcs, each with its own traditional society. Lately, the orcish communities tend to mingle more and more with the non-orcish ones - especially since distinct "human", "elven", and "dwarven" cultures (plus countless others) are slowly merging into a general "humanoid" society. For the people who grew up in the United States, this is kind of like how people from different states might have different cultural values and norms in their own homes and neighborhoods, but can still relate to people from other states without too much trouble. The narrower "Texan" or "Pennsylvanian" identity is only part of the broader "American" identity, and the latter can easily take over when necessary; this is especially true when said people are further united by a common language, currency, infrastructure (such as the highway system), etc.
Anyway, the three main "tribes" are the Vrothgar (mostly Lawful), the Grullgar (mostly Neutral), and the Mithgar (mostly Chaotic). Members of the "tribes" are identifiable by some physical variations, even if they are not active members of the tribe from which they are genetically descended; these distinctions are less visible among those who grew up entirely in the broader "Duemeran" cultural context, and all but intangible among cross-breeds (typically individuals with one human and one orcish parent). Vrothgar society is highly regimented, based heavily on honor and bravery; Grullgar society is less honor-focused, more like the usual informal hierarchies that tend to arise in human and demihuman bandit groups; and Mithgar "society" as such does not exist, for reasons I'll get into shortly.
When I was sketching out the campaign, I quickly decided that I didn't want to have any entire race that is evil. The big reason for that is the racist overtones that would carry, especially if said race is partly or wholly based on a real-world culture, but a second reason is that I don't like stereotypes in general, and more can be gained from being optimistic about human (humanoid?) nature than from being pessimistic. If the goblins always attack, the party just kills them; if the goblins are willing to trade, barter, or even just talk about things the party wants to know, then interesting in-game relationships between different groups can form. (My last AD&D session involved a friendly kobold who was happy to share the abundant food and drink he had found in the pantry, and one of my players remarked afterwards, "That was cute.")
So, why would the Mithgar tend to be more Chaotic in their behavior (Chaotic Neutral, not necessarily Evil)? I thought of a solution: they sometimes practice cannibalism. This does not, in and of itself, mean that a person, race, or culture is evil in my game; after all, the lizardfolk eat their dead, but they're still mostly Neutral in almost every edition of the game. Rather, the Mithgar tendency to consume the entire body - including the brain and cerebrospinal fluid - means that the resultant prion diseases are fairly common. This makes it rather difficult for them to form an organized society, especially since some of the nastier conditions have a chance of being passed on genetically, even before the standard vectors and mother-to-unborn-child infection are taken into account.
I was thinking that this was a way to have a reason for the standard "orcs are evil", while allowing a condition whereby some orcs (actually, the majority of them) could turn out NOT evil. But then the thorny question of nature vs. nurture comes up. Assume that psychologists, sociologists, etc. somehow made their way to Duemerus, and decided that intervention was necessary in order to ensure higher quality of life for Mithgar children. Is their Chaotic tendency a function of their genetic heritage - in which case they would have some inborn negative traits - or of their environment? And if it's the latter, wouldn't an especially presumptuous and egotistical person postulate that the Mithgar culture should be dissolved, and the children raised by "acceptable" adoptive parents?
Most readers will begin to see some major problems with either "solution", in that these types of arguments have been part of real-world concepts like eugenics and ethnic cleansing. And these supposedly "scientific" concepts have done a lot of damage to both individual people and entire cultures; some of these attempts at genocide were, sadly, successful. It's fucked up, and I realize that I've introduced a thorny issue into my game without a good solution. Either the Mithgar's genes are evil, or their culture is. The former is a slippery slope leading to the fantasy equivalent of white supremacist thinking, and the latter, while not impossible or even confined to racial lines (just look at how toxic "gamer culture" can be), brings up the issue of cultural homogenizing that the "assimilated" people (in real life or in Duemerus) would certainly object to - and would be completely justified in doing so.
This is already a campaign where I've introduced such controversial topics as cannibalism, and where I might end up introducing pregnancy and its related controversies in the future (depending on how a similar situation is resolved in a Godbound game I'm playing in... remind me to post about that some time). I realize that it's important to discuss topics like racism and cultural appropriation, but is it right to spark such discussion within the game universe itself? More importantly, will it lead down a road that the players don't want to follow?