But in many other cases they kill things because "they are in the way" like guarding a McGuffin or follow orders to clean out a cave of this or that monster. And such cases the race of whatever you are killing certainly matters. If the PCs are paid to clean out an abandoned mine from dwarves instead of kobolds they will often approach this differently or when the McGuffin they need is worshipped by a primitive tribe of wood elves and not gnolls.
Well, I'd say it very much depends on whether the behavior of dwarves, kobolds, wood elves and gnolls are the same. Do the PCs have any reason to believe negotiation will be successful? Is the relationship that the tribe has had to its neighbors the same in all cases? I got to tell you, but wood elves in my game are very likely to shoot first and assume all strangers are hostile. I've never had wood elves guarding a McGuffin, but that sounds like an interesting scenario. The reason that PC's might approach dwarves and wood elves differently is that they assume that they can.
The real fault here is DMs that refuse to allow solutions other than the ones they envisioned for a scenario. There is no reason that a party couldn't trade with evil humanoids. The real problem is DMs that design combat scenarios or social scenarios and the players are metagaming based on the signals that the DM is sending, but not necessarily for the reasons you think. If gnolls hail the PC's and ask what they want, and wood elves ambush PC's and shoot first, you'll get very different behavior. Even if the wood elves are good and believe that the are just protecting themselves from trespassers. Even if the gnolls are bandits and slavers.
The same way good and evil is assigned in the real world.
Yes. Absolutely. Let's assume that assertion is framing my whole discussion.
And lets be honest, in nearly all D&D adventures it comes down to PCs killing things labled
evil without remorse, regret or consequences.
You keep getting stuck on this word "labeled". And again, the problem you have is that these things that the PC's are killing are not just labeled evil but are evil. And those that aren't evil are usually aggressive and hostile and want to make a meal of them. There would be absolutely no reason to feel regret for killing 95% of the things that my PC's kill, and for the other 5% there is remorse and regret and sometimes consequences.
When the PC's kill they usually have a reason for doing so. I don't know why you think otherwise. That isn't to say that the PC's are always moral paragons. In fact, far from it. But the PC's generally know and understand that they aren't moral paragons, and that they've made mistakes. They do have conversations like, "Are we sure we aren't the bad guys? Because sometimes I think we might be the bad guys."
Still I am quite surprised at the pushback I got here. Why do people react so strongly to the idea that killing an elemental who only minded his own business should morally be considered to killing a dwarf who did the same? Likewise killing orc raiders would be similar to killing gnome raiders...
I at least am reacting so strongly because in my game my PC's do not go around just killing elementals minding their own business. Heck, they don't even kill goblins that are minding their own business - they let the goblin knight go his own way. Heck, I joke with them that they've shown more mercy on hobgoblin thugs than human ones - they've outright murdered at least three human prisoners. They let the hobgoblin prison go on parole with only his promise that he'd get out of town. They have enough problems without picking fights with things that are minding their own business. When they pick fights with things that are minding their own business, it tends to snowball - there tends to be consequences. The PC's shooting first and asking questions latter with the Phanaton definitely regretted it - they ended up in an all out war with them versus discovering (as they did eventually) that they were potential allies and they'd been in the wrong the whole time. All those dead Phanaton were just acting in self-defense, and they'd murdered 100's of them and now they were alone on a deadly island without allies or safe haven. Regret, remorse, consequences.
Yes, killing gnome raiders would absolutely be morally equivalent to killing orc raiders. But how often have you run into scenarios with gnome raiders? And does it really fit the morality of gnomes to be off raiding, plundering, raping, murdering and enslaving their neighbors? But yeah, if the gnomes in the area are in fact cannibalistic, murdering, raping, thieves, then you can bet that when the PCs kill them they won't feel a lot of remorse and regret.
And further, I at least am reacting strongly to this idea that cannibalistic, murdering, raping, enslaving thieves are only "labeled" evil and it is somehow problematic that the PC's should be pitted against murderous brutal raiders and not feel sad about it. In the introduction to "Rise of the Runelords" their is scenario around the PC's finding themselves in the middle of a goblin raid, and the goblins are given personality and a vim and the writers endeavor to make the goblins something other than faceless or bags of hit points. But the writers also do a very good job of making it clear that the goblins aren't only "labeled" evil, and that the are rightly feared and despised.
What I'm reacting to is an implicit statement that unless your game features moral relativism you are doing it wrong, and indeed it's possible that in real life you are immoral yourself.