Yes, have to agree with you about the leprosy being the overarching foundation of the 'ordinary' world theme. I think since the works were released the world's gone pretty crazy about sex offending, which elevates the perversion themes a little more, but only by societal context, for 'now versus then' and not by author intentions.
Having said that, Lord Foul and perversion were where the mythology always took us, when it was about Donaldsonian 'wrongness'. Violations of natural lore and law. Elena had some kind of creepy crack or line, or something in her mind/psychology that surfaced (Cracks of Doom notion?), I seem to recall, three times. Once in Glimmermere, once somewhere else (forget) and of course at Earthblood day and the Power of Command. And AGAIN, Donaldson in the Andelain-ian summoning of the Dead puts Elena into a horrific confrontation with a partly antiposed facet of her nature, some many thousands of years later, with She who Has No Name.
I liked Nick Succorso, who was the archetypal 'bad boi' and Morn using the zone implant on herself for Nick was, in my mind, not quite how that kind of sexual attraction works in mother nature's world. Sexualisation or sexual attraction to Succorso-ites is an anti-social grounding into sensory purpose, an artefact of human condition, yet most usually comes with great emotional pain in unions founded of perversity, ultimately. We see it a lot in medial and remodernisations of old mythologies. Buffy mythology and Spike. True Blood covered it a lot.
I also very much loved Gap Sickness. As Morn blew up her family OMG! I was hoping Donaldson was going to do more with it than he did.
I wonder, suddenly, about the 'null' areas of mind not mapped out by implications of Gap Sickness. I saw the trilogy as deeply reflecting (again spectral) segments of the social mind. The Spectral Mind could most well have been mapped out in a Gap Sickness juxtaposition. I see psychosis or some types of it implicated in some of these themes in our world. It's a condition with so many varied expressions, and each has some snippet, or feature or metaphysical element of many wondrous human mythologies. The shadow cast by Society's dualism in its demarcation of territorial hold over propriety, ideas, and its meritocracy. Deeply divisionist thinking in the Minds of Might of Men has to create Spectral Shadows in social-collective consciousness. Of course, 'real' is not where I'm taking this, at all, although, as one watches mythologies in film (e.g. Star Wars - dualism in good+sexlessness and evil+evil sex in the Sith), the lines traced by fear as one watches such mythologies (especially those with metaphysical overtones), that draws a line of 'effect' or 'direction' to one's one spectrally haunted areas. All humans seem to have them.
Here then - is my join to Frodo and Tolkien's rendering of 'metaphysical evil' and Frodo-ism. I quite agree with you about Frodo's inheritance of the Ring being very significant, and so, the Gifting, indeed, a critical difference in how the Ring ordinarily works in the Sauronic sense. I'm sure Sauron crafted it as Sméagol's claiming of it shows us. Strangely - Holbytlan folk all through. Sméagol succumbs upon finding it in the battle with Deagol. Yet, Frodo and Bilbo - some 4000 years later - the closest we got to dire battling was in Elrond's halls. And there, we certainly saw the Spectre (Spectral* Theory is one of my new areas of thinking), of Frodo's "Sauronisation".
The author placed us in Frodo's narrative, viewing Bilbo. I have never been quite convinced that what Frodo saw, did not reflect, in part, Frodo's Shadow. Shadows, as we know, via Tolkienism - it's an important theme. In its inverse, I've always never forgotten: ringwraiths and how the living "cast a shadow" in their minds.
That one's 'tricksy hobbitses'. How does a being OF Shadow (Spectral--The Spectral hue of the ghosts of the Middle-Earthian 'good', created by Sauronisation), have a SHADOW cast in its mind????
This, must mean then, for Frodo, viewing Bilbo as Frodo saw a SHADOW of Bilbo lurching in greed and avarice for the Ring--and given Frodo's recent recovery (recall his 'transparency)--it was from there forwards that.....
I never quite trusted Frodo, and I somehow knew there was something at work. He was too quick to volunteer to take the Ring to Mordor. Seriously? He what? After just recovering?
I never trusted the volunteerism from its root. Here, then, my connection to Donaldson as he says "Frodo creating Sauron"....
Footnote:
* Spectral-definition as I use it. The metaphysical dimensions [i.e. 'magic', 'spirit', 'lore', 'spirituality-KINDS'] of collective-social trends, collective beliefs, and the shadows cast by the collective religions that split the universe into --OFTEN --Good versus Evil. A Spectral 'line' or 'layer' or 'level' or 'dimension' can be 'element-ised' [FIRE WATER AIR], 'matter-ised [e.g. FLESH, CYBORG, UNDEAD, UNFLESH, ZOMBIE] if about 'living'. Or it can be matter-ised [Rock-Earth-Elements of Period Table-magic-ised, e.g. 'living stone', 'haunted geo-spiritual 'earth' foundations. Rips in 'time' created by 'new undiscovered elements'--that one's UFO-isable. The Amnion come to mind. They can also be CREATIONIST - 'Elves' 'Ea', and that draws a line to Science and the opposite of Entropy, whatever the heck that might be]. etc
Example:
The Spectral ghost of spiritual beliefs that place 'sexuality' with evil and 'asexuality' with good:
An example is Succubus and Incubus, or Lileth - which are Spectral Shadows and sexualised fears as they caste into cognition, for the Western religiosity, in particular.