Agressive and Non-Agressive to NPC's

There should be a thing like a button or something to switch your aggro to let you attack NPCs or to let your weapons and attacks ignore NPCs.
Because I have killed alot of my npcs either by misclicking or by trying to protect one from a random monster, heck even making a MOD of this would be appreciated ._.

 

Or at least they should ignore your weapons if they are being attacked by monsters.