I was planning to make a profound research upon the subject, but get lost in flow of events IRL. Still more it's interesting to watch the development of discussion then give anything ready-made. So, here is the statement to be discussed:
all millers in JRRT's works are nasty up to some degree
as a back up - Ted Sandyman and the Miller of Farmer Giles of Ham
possible reason: two millers (White Ogre and Black Ogre, if I recall correctly) feared by Ronald and Arthur in childhood
go ahead folks