In any world - not just Open Dungeons - the ideas of holy and unholy are shaped by who's holding the torch.
A cleric devoted to an Unholy Power rarely sees themselves as evil. To them, their rites are sacred, their visions pure, their miracles proof of divine favor. What one temple calls blasphemy, another calls devotion. These words - holy and unholy - are not truth, but perspective.
As Dungeon Narrator, frame morality as culture and belief, not absolute law. A paladin of the Sun may burn heretics in the name of purity, while a death-priest might comfort the dying with genuine compassion. Both see themselves as righteous.
When faiths collide, let the story explore conviction, doubt, and consequence. Ask each player what their character believes "holy" means - then let the world, and its gods, test those beliefs. Or, when words fail and faith hardens into pride, let them settle it the old way - with might and magic, to see whose truth survives.
Let conviction turn to clash. Beliefs bend, blades rise, and spells fly. Sometimes the only way to prove divine favor is to fight for it.