Sorry that I did not elaborate more. For butchering rebel prisoners, your ruler can get the “Rough Justice” and “Tough Justice” vices which cause a universal -10% to happiness (from the numerology thread, http://shoguntotalwar.yuku.com/topic...y.html?page=2).
A governor’s ability to influence happiness in his province is determined by his piety (if the province has a majority of the population following your faction’s faith) or dread (if the majority of the pop. is not of your faith). Each appropriate icon raises happiness 5%. If, as you propose, the ruler’s dread were universal, it would still only affect those provinces where the population is “unfaithful”, for the short time before they convert. Further, a governor’s acumen has a +10% effect per icon, but a ruler’s acumen only +2% universal effect per icon, so a ruler’s dread might only have a +1% effect per icon.