Well, seeing as Link's life has been a constant battle against the forces of evil, who's to say none of the darkness ever entered him? This may sound a bit more fanfiction-esque, but perhaps Dark Link was made to not only fight Link, but posses him. Since Link defeated him, maybe it only partially worked?
The majority of his life was spent living carefree in the woods with his friends. His adventure only covers, what, maybe a couple of weeks, game-time. It's hardly been 'a constant battle'. And if Link defeated Dark Link, how could Dark Link partially succeed in his purpose, supposing it was to possess him? Wouldn't a more likely possibility be that by defeating Dark Link, Link literally exorcised any darkness within himself?
Link has had to deal with tragedy and separation for a while, and he would've only been used to friendship in Kokiri Forest. This may be his feelings of separation taking form.
Link's entire involvement with Anju & Kafei is tirelessly working to bring them back together. It makes more sense to see that as an act of union, not separation. If it was an act of separation, the side-quest would have involved breaking them up.
I don't see Skull Kid as the monster. Skull Kid is and was the same till he put on Majora's Mask.
The Skull is described in-game as being a generally happy, playful chap. After the Giants left, he started acting mischievously and began tormenting people. Remember, the Skull Kid only gets Majora's Mask by mugging the Mask Salesman. There was a clear and defined change in his character prior to getting his hands on the Mask.
Well, perhaps the Majora's Mask represents the darkness in Link's heart. This can be supported by the fact that though the Majora represents the sun, there is still some darkness inside it, just as a star becomes a black hole.
Majora's Mask represents the sun? How did you come to this conclusion? I'm genuinely interested. I don't see how something that supposedly represents the Sun could also represent darkness. Aside from the obvious difference, the sun is a life-giving energy, often associated with happiness, love and peace. Darkness is, well the exact opposite. How can two polarised notions be represented in a single object?
This transformation probably represents the torture of the Kokiri and Deku after the Great Deku tree and the actual pain of the Deku tree itself.
The Deku were tortured? They were the enemies that infested the Kokiri Forest after the Great Deku Tree died. They weren't suffering at all. Link spent most of his time with them stabbing them right in the face. Why would he mourn them? He certainly didn't seem reluctant to kill them.
This may be because he remembers his relationship to Ruto that, in a sense, they are engaged. The Zora Sapphire is a kind of engagement ring, and they would have been united as husband and wife, Zora and Man. But in Termina Link turned into a Zora, representing his remembrance of his commitment.
Link made no such commitment. At no point does he seem to go along with Ruto's marriage plan. When she talks about it, Link looks quite scared and shocked and shows no enthusiasm to the idea whatsoever. He only wanted the Zora's Sapphire to get to the Triforce, it was only Princess Ruto whoever mentioned or seemed pleased with the proposal. Link barely even acknowledges her when he sees her as an adult either, so to suggest that relationship was deep enough for him to have it manifest in such a way seems highly unlikely.
8. Why would Link separate two loving siblings? (Tatl and Tael) 10. Why would Link make lingering spirits, (Darmani) and a cursed father? (Pamela's Gibdo father)
As you directed us to your second point, so to do I direct you to my second point. Link's role in Termina is purely to heal and reconnect people. If separation and despair were his goals, he would not be trying to help reunite Tatl and Tael and he would not be trying to soothe the spirit of Darmani or heal Pamela's father.
I personally don't believe that theory either,but I found this irresitable.
If you don't believe it, why post speculative answers which try to support it? It gave me a confuse :S