If u use the Mod WARZONES - Civil Unrest by MyGoodEye (u should its a great mod) ppl get pissed of when u kill faction members ... even if u do it when noone see it. So it can happen walk in whiterun hear heimskr and accidentally hit him with an sword when nobody look but the complete town hate you (accept the guards who ignor you) even the jarl etc attack you.
This mod simply remove the faction from Heimskr so you can kill him... and make him more ugly so its a joy to kill him ;P

for all who are stunned by my unbelievable Moding skill and english knowledge ;P
all credits go to Skyrim NPC Editor 0_67 by foretrenty and my saxon english teacher;P