Elements of Evil: Fire and Ice, North and South

Have you ever thought about how Morgoth's stronghold was located in the far north surrounded by bitter cold while Sauron's was in the south-east in a land parched by the heat of volcanic activity? I think there are a few reasons Tolkien may have written these two villains living in extreme environments.

First, anthropologically speaking, living in a temperate environment is easier, therefore attracting more people. Secondly, since Tolkien wrote his Legendarium as a myth for England, it would make sense that the good guys would live in a temperate environment such as England. Thirdly, this may have been a philosophical metaphor for the way to live. Ancient philosophers championed the "golden mean" as the way to find harmony in life. Aristotle said, for example, that courage is a virtue but too much of it produces recklessness and too little, cowardice. Many religions also preach that evil resides in extremes so living moderately is ideal.

The two most evil beings in the Legendarium thrive in extremes. What are your thoughts on why?