Not just simply evil

To frame this all up - here is my 'philosophy of D&D alignment'. The internet being what it is, let me first state that what you read below is my view. You run your table in a way that works for your table. What I am talking to here is what I have come up with from my time running tables, in particular Planescape games, to make things make sense.

I come to this from reading the online discussions that build off the premise of some sentient races being essentially evil. I find myself looking through a window into a variant of the game that I do not recognise at all. The idea that you just plough into other sentients without accounting for why they are doing what they are doing makes no sense to me and never did. I could happily play Heroquest (kick in the door, kill 'em all) but as soon as I had a copy of the old black box, I was trying to figure out the why's of the dungeons. Someone had to be eating something, the water had to come from somewhere. Things had to make sense. Similarly, if there were things living down here, unless they were oozes or the undead or some sort of magical construct, there had to be some sort of sense to their actions.

For as long as I have been running games I thought it was unfair to the players to have the opposition, who ever it was, just be randomly doing things. Without a driving motivation the players could figure out there was no way for them to outsmart the foe. If the goblins are scouting for food, bribe them to your side with rations. Maybe something is so aggressive they will be unflinchingly hostile - the ogre is going to attack immediately if you trespass in his territory - then you can work around that by avoiding the ogres patch. You could also kite the ogre out of position if you *know* it will attack whomever it sees. The idea that sentient monsters are up to what they are up to because they are simply evil just seems a massive wasted opportunity.

The set-up I use is basically four-fold:
First, in the absence of sentience, we have nature "red in tooth and claw". Predators and prey are guided by instinct, with no place for good and evil.

Next there are sentients, those with the awareness and free will to choose what they do. They may choose to act in a good or evil (or lawful or chaotic) manner. Broadly, I map good and evil to altruistic/constructive and selfish/destructive behaviour.

The next group are created sentients, who are the crystallisations of anothers decision to do good or evil. Their freedom to think and choose is also their freedom to defy their creators conditioning. Here we have something completely outside our own world, our own realm of experience.

Finally the gods, who exist as mirror and amplifier of their worshippers. Some primordial and absolute, others acting as an exemplar of a group. The choice to worship and abide by the ways of whichever god is a free willed choice, though possibly difficult due to community pressure, lack of knowledge of an alternative, etc.

So thats my frame for how my game worlds work. I think it not necessarily a clear match to the ambiguous descriptions in the 5e PHB but is more or less as described in the 3.5e PHB (pp104) - ""Good" implies altruism, respect for life, and a concern for the dignity of sentient beings" [...] "Evil" implies hurting, oppressing and killing others. Some evil creatures simply have no compassion for others and kill without qualms if doing so is convenient." At the root good and evil springs from the choices made by those who are able to make choices; as long as members of a group can make choices than they are neither intrinsically good or intrinsically evil, their choices and actions are good or evil.

Non-sentient undead like zombies - these are a manifestation of the necromancers choice to create them. A warband of orcs has the individual choice to do what they do. They may be plundering and pillaging and murdering people in cruel and horrible ways - but they are choosing to do this, they made the decisions to raid, they own the consequences.

There may be groups that appear evil. Members may place no value on the lives of strangers, or may raise its members to be cruel and uncaring, they may work tirelessly to eliminate their foes and so may look evil to all outward appearances. Similarly a group may be some manner of supremacists that accept only members of some species or race and so appear as if all member of a species or race act terribly towards others. This is not intrinsic to the members of the group, it is a choice they are making. The changeling-snatched child raised in the Feywild will have a very different take on things.

Some thoughts that I felt expressed the point reasonably well were:
"There's also rivals, unscrupulous competitors, dangerous cults, and so on and so forth that can... wait for it... be from other intelligent species in the game, be killed, and not paint the whole species as being self propelled pop-up targets for adventurers to attack." [POCGamer]
"the game functions perfectly if individuals, but not whole races, are evil. You can still have evil people, evil gangs. You don’t need evil babies, or people savage because of race. That makes the game & community less inclusive. & it’s lazy storytelling."[Arcanist Press]

What I particularly don't understand - and this may be a function of my original play tables - is that the sentience or lack thereof, the intrinsic evil or not of the opposition to the players made no difference at all. A long running Planescape game featured a core of the party built around devotees of Ares; glory in battle was an end to itself. Whoever they were, if someone drew steel, they got killed. Another Planescape game featured the clean-up squad of a deeply amoral trading house; they completed their contracts, scrubbed off the blood and slept soundly afterwards.

Another problem I have with 'things are inherently evil, kill them on sight' is it makes everything a slug-fest. There is no reason for it not to all be undead - faster or slower zombies, but in the end just hordes and hordes. The party may well triumph over truly frightening odds but 'repelling the oncoming horde' is just one game and I don't fancy running and re-running that same campaign forever.

I played a very enjoyable Living Arcanis campaign where everyone was human; the drivers of conflicts were the gods people worshipped and the nations they swore allegiance to. No need for 'intrinsically evil' opposition. This post on Inverted Fairy Tales gives a neat set of examples of conflict and adventure hooks that have no need of corporeal monsters beyond the undead; the antagonists are magic users, curses and power-politicking humans.

To wrap up, I think you miss great feedstock for campaigns when your opposition is unthinkingly evil. You get much better mileage from going 'what is driving this foe to be here, now, seeking what it wants' - because once you have that, the adventures write themselves. They can be wicked motivations, they can be greedy and grasping, callous and cruel - but something drives them more than 'they are evil'. At my tables, in any case.