“Systematic textual analysis of The Hobbit supports our initial hypothesis that the triumph of good over evil may be assisted to some extent by the poor diet and lack of sunlight experienced by the evil characters,” write Dr. Nicholas Hopkinson of Imperial College London and his 15-year-old son Joseph Hopkinson in the current Medical Journal of Australia. They take advantage of the special Christmas edition of the journal to posit a physiologic contributor to a timeless duality at the core of fiction (and life), and why good characters tend to win:
A striking feature of fantasy literature has been the consistent victory of good characters over bad. While the consensus has been to attribute this to narrative conventions about morality and the necessary happiness of endings, we hypothesized that a major contribution to the defeat of evildoers in this context is their aversion to sunlight and their poor diet, which may lead to vitamin D deficiency and hence reduced martial prowess.
... Gollum, himself “as dark as darkness” lives in the dark, deep in the Misty Mountains. He does, however, eat fish, although the text describes these only as “blind” and it is not clear whether they are of an oily kind and thus a potential source of vitamin D. He sometimes eats goblins, but they rarely come down to his lake, suggesting that fish play little part in the goblin diet. Interestingly, these occasional trips to catch fish are undertaken at the behest of the Great Goblin, leading one to speculate that his enhanced diet may have helped him to achieve his preeminent position within goblin society. In due course, the Great Goblin is replaced by the Son of the Great Goblin. While simple nepotism is a likely explanation, we are unable to exclude an epigenetic process whereby the son’s fitness to rule has been influenced by parental vitamin D exposure.
Their analysis is also an opportunity to remember that evil people in your life may just have a garden-variety vitamin deficiency or hormonal imbalance. You don't have to be afraid of them. Are they evil because they live in a dark cave, or do they live in a dark cave because they are evil? Does it matter? Assume the best and offer a fish. If you get eaten, you get eaten.