Nope. It's what good PCs do in the assumed world of D&D.
No, it's not. Good PCs dont engage in genocide.
Sure, as an extreme exception to the standard alignment so extreme it's that noteworthy as an anomaly.
Rubbish. Read the rules bro. Orcs and Goblins are only normally evil because their society (driven by their Gods like Grummsh etc) tells them to be.
If an orc is separated from its cruel gods and its society, it will not be inherently evil. Mike Mearls even said,
“But if you took an orc and raised it in human society, it would just be like a human. Obviously it would be orc biologically, but […] there's no reason why an orc couldn't be raised [that way].”
Those Orcs could very well be disillusioned with the Orc pantheon, and only in the dungeon to find a better life for themselves (Neutral) after leaving their tribe.
Nope, you left out a crucial element of what I said. I said ARMED. When you come across ARMED goblins and orcs in a DUNGEON, you ASSUME they are evil because they 99.999999% of the time are. I am not in fact saying you kill unarmed civilians.
Coming across armed Orcs or Goblins in a dungeon is not reason to kill them out of hand. You gain your reason to kill them, if (and only if)
such force is reasonably needed to protect yourself (or others) from harm from an imminent threat, and is proportionate to that threat.
If those Orcs ARE in fact armed, and they DO in fact pose you an immediate threat that requires lethal force in self defence, then yeah - hack away. The alignment of the Orcs has nothing to do with it.
Paladins carry swords for a reason.
Again, what I am describing is in fact the baseline assumption of this game
No, it isn't. For you perhaps.
But if the Gods of Good in your games are down with genocide and the wholesale slaughter of a people based on nothing but the Race of your victims, I shudder at the atrocities that one could commit and still get into 'Heaven'.
I don't think it would be an improvement as you'd have to use your first action to attempt to negotiate every single encounter to see if you've run into the unusual neutral or good armed orc or goblin only to find you're getting smacked with a sword or struck by a arrow most of the time.
What on earth are you talking about? Why on earth would you need to first attempt to negotiate with something that is trying to kill you (or just about to)?
If you wake up in the middle of the night and see an armed intruder in your home, you dont have to talk to them first before shooting them. You can use whatever force is reasonable in the situation to protect yourself and your family.
If Police see you with a knife running at someone, they are not going to try and talk you down (unless they have enough time of course; in which case you'll get a 'Stop or I'll shoot!'). They're going to shoot you dead.
If you're in a dungeon, and armed or hostile ANYTHING (from Orcs, to Paladins to Dragons to Golems to whatever) come at you with hostile intent, you're within your rights to resort to reasonable force to stop that threat (this includes lethal force when warranted). You dont have to engage in a pleasant conversation first, issue a warning, attempt to negotiate or any thing of that nature (unless of course the threat is not imminent, and the use of force is not reasonable).
The instant they attack (or look like they're going to) reasonable force to protect yourself, or others, is OK.
If you walk into a room and see an unarmed Orc woman, cowering by her bed next to several Orc children, you dont just walk up and bash her (and the childrens) heads in with a hammer. If she suddenly reaches for a weapon, stab away.