Except that the standard D&D world is more racist than Delhi, Jo'berg, Sydney, or Atlanta in the mid 19th C. The thinking and feeling beings that are listed as monsters are non-people in the games, and, at least in AD&D, are inherently evil, irredeemably so it would appear, so killing them is merely preventing their spreading their evil ways...
... in the context of D&D as presented, Orcs not even good as slaves. Hence, slaughter is the order of the day, Given that the treasure in lair is where the bulk is, bypass the warriors, kill the orc village while the warriors are out, and get out with the treasure. If possible, tuckerize them before they tuckerize you. wait for one to be alone, and remote slay. If high enough level, cloudkill and a couple fireballs can end most villages. Maximum XP for minimum risk.
This does not really jive with the modern presentation of the game either as realized by Fifth Edition or especially Pathfinder Second Edition. The latter of the two goes to pretty explicit lengths that the defensive killing of orcs who are reaving is acceptable (just as it would be with humans), but that slaughtering them in their own territory when they have not been aggressive is not.