Picture it: you're coming up to a bandit fort with your weapon drawn, the bandits stream out, you close for the fight... and suddenly the bandit decides that deer on a faraway hill must die right now. Off he runs, yelling obscenities and threats at a deer. It's funny/annoying but I got tired of it.

This situation happens because Bethesda set the aggro slider to "very aggressive" on bandits and other baddies instead of bothering with the faction system the game has. This makes a NPC to murder anything not directly allied to its faction, and from there it's a crapshoot as to what the AI actually decides to target.

So let's fix that. And break other stuff.

WHAT THIS MOD CHANGES:

First, 14 edits to factions, here they are in a nutshell:
Bandits faction: hate all, and are hated by all.
Vampires faction: hate all, and are hated by all, except some animals.
Warlocks + Necromancers factions: allied to each other, and to not much else.
Forsworn + Hagraven: allied to each other, and not much else. Hate spriggans, love goats.
Guard faction: a bit more expressly aggressive versus monsters and predators.
Dawnguard: mainly busy fighting vampires but not above a little monster hunt.
Dragonborn Cult: mainly interested in you, but hated in Solstheim and by guards (nearly unchanged).
Civil War factions (Sons + Empire): will take some time out from murdering each other to murder a monster but mainly busy with that war thing.
Companions: will take on anything and defend the citizens.
Vigilants: mainly interested in Daedra and Dremora but will stamp out evil wherever.
Thalmor: not much changed yet, needs more quest testing with current settings.

Second, it resets the baseline for aggro on NPC records for all vanilla bandits, vampires, warlocks, necromancers, forsworn, hagraven, cultists to "aggressive". This will cause those factions to attack enemy factions but mostly ignore neutral factions (which is the default faction-faction state).

Finally, for the changed NPCs, because they are no longer blinded by rage their "confidence" setting comes into play (think of it as "courage"). The majority of bad guys are still the "fight to the death" maniacs you know and love to kill. But some will recognise a stronger opponent and try to evade combat, and some will flee when the tide turns against them. They may come back with some friends.

WHAT THIS MOD DOESN'T CHANGE:

This mod will not fix all issues with bad guys fighting "the wrong target". Some bad guys have an 'aggro radius', meaning they will threaten and only fight if you get too close. You can see this in vanilla wolf behavior, and many bandits occupying castles have the same settings. If some hapless deer breaks that radius, it's going to die, and because bandits are all buddies, the rest of the bandits will engage too. This is normal. BUT since the deer is a neutral faction and you, the player, are hated, they will switch targets much quicker and generally be better at keeping focus in a fight. Not perfect. Better.

I did not change the undead who hate all life and the falmer who hate all surface life. They will indiscriminately murder anything and everything (as before). I also did not touch any animal factions as there are plenty of wildlife mods out there already doing a much better job than I ever could. I did not change any other settings outside of the scope of this mod as outlined here.

This mod will not change any bad guys added by other mods, separate patches will have to be made. I'm working on a SIC + OBIS patch, since I play with both mods installed, but any patches beyond that will have to be made by the community. I'm happy to host them on this page, ping me if you have one ready.

WHAT THIS MOD BREAKS:

No idea, there are thousands and thousands mods on the nexus, countless vanilla questlines and quite a few mess with factions at some point, so I'm sure something somewhere will break. Make a save before you install this mod. Overall, any breakage should be easy to roll back.

INSTALLATION:
Drop in your data folder/install with your mod manager of choice. Suggest somewhere near the end of your load order.

UNINSTALL:
Go to an inside cell with no other NPCs. Make a savegame. Exit thegame. Remove the mod. Start the game. Load your savegame. Carry on.
This mod has no scripts or fancy bells and whistles.

COMPATIBILITY:
This mod changes 14 vanilla factions, many of which are not generally used by other mods. Changes a bunch of generic/unnamed bad guys NPCs.
Other mods which add more bad guys will need to be patched if you want the same behavior from those NPCs. A patch for SIC + OBIS is in the works.