Death is temporary. If before you kill the guy all he is doing is skulking around the desert acting like a thug, sending him to the afterlife make do him some good.
Quote:
Show me where Alshain said to go murder people just because they are not of good alignment? You won't find it, because it doesn't exist.
Quote:
Honor the White Flame through purification in seeking to cleanse the world of evil.
Crusade always against the wicked who fail to see the light of the White Flame.
Trust the White Flame, as He may come to judge me.
I believe this is wide enough of a command for interpretation and equivocation.
Additionally a principled character is not taking gear for "selfish" reasons. His life is devoted to his virtuous cause and anything he has is used for that noble purpose.
Lastly, beating someone up, taking the gear, but sparing the life can be considered even more cruel. Killing the guy who has not accepted Alshain into his heart may bring him redemption through rebirth. (and if not, then the world is better off without him)
If you want to make the game more realistic, we should be buying our gear from reputable craftsmen who continually pump out more as it gets broken, not killing evil people for good gear.
A real principled adventurer would have a rapport with a good craftsman of adamantite (there is plenty of adamantite ore available) and would be equipped at all times, not begging old paladins or wearing armor previously worn by undead wraiths.