I understand that most of the monsters in D&D are monsters in the true sense, inherently evil for the sake of being evil (an orc gets off on killing the village).
But if you take the idea of "evil is as evil does" away, blur the lines a bit, I think it can be an interesting way to turn the tables in your campaign. What if orcs do what they do because they are the "indians"? The indigenous race that has been getting the screw job by the "others" (to use a Lost-ism) for the past few millennium? Killing a village is not done out of evil a but as a matter of survival. Suddenly your band of human "hereos" stops looking so heroic and starts looking like group genocidal maniacs.
Eberron leaps out at me again.
In part, because Eberron is happy to have "noir"/dark heroes who do awful things in pursuit of their goal, which can be of dubious justice. You're killing all the orcs so they won't kill the settlers, but should the settlers even be there in the first place? What if the settlers are being driven into orc lands by famine in their own? What causes that famine? If it's nature, how do the PC's broker a peace? If it's something more sinister, can the PC's reverse the process by killing the source?
I know in my campaigns, for my "mortal" enemies, I like to give them clear motives that are sympathetic and understandable, and leave it to my PC's to pick a side. I recently had a town falsely accuse some refugee orcs of kidnapping a girl, and had the PC's find those orcs robbing peoples' houses. The orcs claimed they were just trying to survive (they're refugees from their own land, they need food and blankets for the winter, but obviously no one in town is really willing to work with them, so they have to steal), the townsfolk claimed they were justified in working up a mob to kill the orcs (that girl disappeared, they were hanging around stealing stuff...), the PC's had to decide which side to take.
Most humanoids fall into this for me. Orcs IMC aren't inherently evil any more than elves IMC are inherently good. This was true in 2e, in 3e, and still in 4e. There might be some cultural tendencies -- orcs tend to reward selfish self-interest and petty violence and rage, while elves tend to reward virtue and helping those less fortunate and putting an end to destruction and collapse.
The Law/Chaos axis in D&D was also pretty good at exploring this, especially when cast as "civilization vs. wilderness," where you had wizards and artificers and fighters and paladins and the like upholding the tenets of public virtue and civic pride, and you had druids and rangers and sorcerers and the like upholding the virtues of personal autonomy, freedom, and relativism.
And, yeah, the genocidal maniacs angle is something of an issue for D&D in general, and has been forever, largely because DMs will define different things as Cosmically Evil (in one campaign, orcs are, taking after Tolkein; in another, they aren't, taking more after WoW, for instance) IMC, because I make it clear that "evil isn't always Cosmic Evil, and sometimes you'll fight and kill things that aren't EVEN evil" (unaligned and good enemies both make common appearances), it doesn't become a big problem, even though my orcs and goblins and the like have more Eberron or The Horde or "DM has a degree in Cultural Anthropology" in them.
Extermination of any kind of creature -- even the cosmically evil ones like devils -- is out of the hands of any one group of adventurers.
As for the shark, yes in 2009 we can watch Discovery and know that a great white eats a surfer beacuse the surfer on a board looks like a seal from below. But as little as 100 years ago I assure you the average human probably consider the shark evil, a killer that served no good purpose on earth. When I was a kid, I had a neighbor who killed any snake he saw, even harmless garter snakes. This guy was smart, went to the same school I did, but unlike me believed snakes were "of the devil" and needed to be eraticated. Ignorance is one explaination for a perspective on "evil". Your highly evolved predator is another man's monster.
In the Real World, the line is certainly muddied as a whole (though it might be crystal clear for any individual). A creation of fiction (like D&D orcs) has the luxury of actually defining what (if anything) is "of the devil" for itself. Necromancy can just be a sort of cheap way to make "robots" in a fantasy setting. Swearing a pact with the setting equivalent of Satan to gain Warlock powers doesn't always have to mean you're evil, either. Even if your ancestors did it long ago and you're a tiefling. And the game is going to reflect modern cultural mores, which, these days, include a healthy dose of "No person is created Evil, they are made that way." So it makes sense for Orcs (which seem to be "people" as presented in D&D, rather than artificial horrors) to be made evil by society in things like Eberron and WoW, rather than created evil as they were in LotR (which took a much more mythic view of the creatures which served Cosmic Evil).
I guess embracing cultural relativism is just something I do automatically in my games, to a large degree. I think a lot of players are similar. They'll have their Lord Voldemort and their Emperor Palpatine and their Sauron, but they'll also have legions of "humans in funny suits" that are other humanoid races, which, other than looking different, have no more mental differences than some guy from Sweden and some guy from the Congo. I personally like embracing that wide middle ground and working with scenarios where there is no clear Evil, and having the PC's choose between basically their preference, or whoever has the most persuasive case.
For me, the ingrained alignment of previous editions didn't prohibit that at all. Even if something had the alignment Chaotic Evil, that didn't mean it was CE to its core -- alignment was a descriptor, a way the universe attributed sides in an ongoing struggle, and it, for most creatures, was fluid. I described it as four different kinds of "alignment particles" that worked like an energy in my settings. Some people were saturated with it, others had a thin patina of if, and there were creatures (Demons, devils) who were MADE of it.
That's why Tieflings, IMC, had an interesting dillema. They were, in part,
made of evil, as if evil was a substance, a physical thing, and tieflings were composed of it turned to flesh and bone. A tiefling's struggle was to be one with its natural evil, or to try and saturate itself with some other alignment enough to change its very composition.
