Madara is a Master Psychologist
Many are thinking that Obito turned evil becasue of Rin. While I agree her death is the catalyst, the last straw, i think we are missing the big picture of what has happened to Obito and what Madara is doing to Obito. I believe the way Madara has gone about turning Obito is the real reason why Obito goes along with the Moon eye plan and goes evil.
Madara is one uber psychologist, and here is why I say this:
Let me start off by saying madara is not asleep in chapter 603. The appearance of being dormant is part of his plan for converting Obito. More on that later.
For now, in chapter 602 Madara planted a seed (no pun intended) in Obito by telling Obito about his grand plan to bring peace. Obito thought nothing of it, shrugged it off really, it was just some old man's crazy dream. Obito is more focused on getting back to his Team. This is madara's 1st mind game with Obito, tell him his plan from the beginning knowing Obito would reject it.
Now in chapter (603) Obito's rehabilitation begins. I had thought this before like many others but now kishi confirmed it. Obito's sole motivation to get healthy is to see Rin and Kakashi. (Sidenote: I laughed seeing obito train because I kept imagining "eye of the tiger" from Rocky playing in the background. Anyone else?) In any case, his thoughts while training were of his teammates and more importantly his love/crush Rin. Seeing them again brought Obito hope and strength, which are 2 common themes in naruto. Unfortunatly, this will be his downfall.
While Obito's training occurs, madara appears to be "asleep". But he isn't. That too is part of his plan to turn obito. Let's call it step 2 in his psychological plan. Madara does this for several reasons:
1. To let Obito feel secure. No madara looking over Obito's shoulder. He allows Obito to think he can train without Madara knowing.
2. To allow hope of escape to grow in obito. And this hope gives him motivation to train and become stronger. (see above rehabilitation/motivation explanation) An Obito with no Hope is useless.
3. Madara"s leaves zetsu (zetsii for plural I guess) to attend to Obito. He left zetsu in his place for the following reasons:
a) So obito has company. If madara would have left obito completely alone, he could have escaped or maybe even gone crazy being in solitary confinement. A crazy obito is of no use to madara's plans.
b) To keep obito informed of madara's plans and to convince obito madara's intentions are good. This keeps the seed that madara planted in chapter 602 growing the back of obito's mind. Zetsu even plants another seed in Obito, that Dream world can revive the dead. And yet again Obito does not care about this.
c) To be used by obito (mask zestu) when the time arises. Make no mistake, rin and kakashi being attacked is part of the plan.
d) I think its no mistake that Madara left 3 Zetsu in his place, in a way they replace Rin, Kakashi, and the 4th. I think Mask Zetsu represents Kakashi, Obito and Mask Zetsu have that rivalry relationship, Mask zestu even flips him the bird. The other Zetsu in chapter 603 represents Rin, remember he starts to say the same words as Rin (We are here to watch you). The 3rd Zetsu represents to Fourth i believe, he one who has been like a teacher, mentoring him (although we never see the 3rd Zetsu). These 3 Zetsu are here to make Obito feel somewhat at home, in terms of having similar relationships around him.
To recap, so far Madara has allowed obito to have hope in seeing his friends again, he has given him companions (3 Zetsu) to keep him sane, to motivate him to become stronger and continue to talk to him about Madara's plan, and he has given Obito time to heal, recover and let the seed (mooneye Plan) grow in Obito's mind.
Now its on to the next phase: crush obito's dream and replace it with madara's dream (Moon eye Plan).
In the end of the chapter, a zetsu appears and gives obito news of kakashi and rin being in danger. They are attacked by Mist village ninjas. (Wait a sec wasn't the mist controlled by madara at some point?) Why, yes it was. Madara has set up the battle that will have Obito witness Rin's death. And madara placed mask zetsu there to help obito escape and see it happen.
Watching Rin die and witness kakashi not able to keep his promise will destroy Obito's dream/hope. Obito essentially put all his hope into one basket, Rin. He trained and got stronger with the sole motivation of seeing Rin again and being with her. And now she is gone, his reason for living the past hower long is gone, what does he have to go back to, nothing. Madara did not take away his, he took away his hope and dream. This is what drives Obito evil so to speak.
Rin's death really does 2 things for Obito:
1. Awakens the latent power of his Sharingan (Kamui)
2. it reminds Obito of that old man's plan (Madara) for peace Chapter 602 and what Zestu said in this chapter: It can even Revive the dead.
So now Obito's dream/hope of being with Rin has changed to using the Moon Eye's plan (Madara's Plan) to revive Rin. Madara knows that taking away something from someone (hope from Obito) is useless unless you have something to fill the void (Moon eye plan to bring peace and revive the dead).
Madara also needed Obito to come to the conclusion of the moon eye plan on his own. He knew Obito was rebelious (what teenager isn't), and if he tried to force Obito to help, it would not have worked. So Madara had to find a way to let Obito think it was his own Idea to go along with the Moon Eye plan. Madara the Master pychologist at work.
Now here are some questions to ponder on my theory:
If Madara wasn't sleeping what was he doing? I believe the body that was sleeping was not Madara's actual Body, perhaps just an outer shell that looked like Madara, or a Zetsu that changed into him (maybe the third Zetsu that was supposedly outside). The real Madara was outside the cave, keeping his plans in motion. This chapter has to occur in the time period that Madara was secretly in control of the mist, and he set up mist Shinobi to be where Kakashi and Rin were going to be. Madara's plan was to kill both Kakashi and Rin so that Obito would be devastaved. But Kakashi survived somehow, maybe by Obito saving him even. This would explain why Obito does not fully blame kakashi for allowing Rin to die, because he is partially at fault too.
And this leads us to the next question:
What were Kakashi and Rin doing that they were attacked by Mist Shinobi? Kakashi is good Shinobi, and he is not going to just fall into a trap, and I don't believe Rin and Kakashi were attcked by Mist Shinobi while in the the Fire Country/Leaf Village. They were on a mission together. I'll have to research part one/early part 2, but weren't Kakashi and Rin both Anbu memebers? If so, Madara somehow made sure that both Kakashi and Rin were on a mission together where he could attack both. Madara set up the situation so that Danzou or the Hokage (we do not know if Rin and/or Kakashi were regular Anbu or Root) was forced to send Kakashi and Rin based on their unique abilities. They were only ones who could get the job done so to speak. The outcome of this mission was Rin's death, Kakashi and Obito's receiving their MS ability Kamui, and Kakashi quiting Anbu/or being dismissed from Anbu and returning to be a Jonin.
There was a thread I saw this morning that i liked but I can't find it again. But here is a summery of the the idea behind the thread:
Orruchimaro wants 1st Hokage DNA
Zetsu wants Kakashi and Rin for the slaughter
Orruchimaro and Zetsu make a deal
Danzou wants Sharingan and 1 Hokage power
Orrochimaru and Danzou strike a deal
So, Danzou gets Orrochimaru to make him stronger, Orrochimaru gets the DNA he needs, and Zetsu got Rin and Kakashi where he needs them.
Now I didn't completely agree with the theory, because I don't think Kakashi was ever a Root member, he was Anbu chosen by the Hokage. I just don't see Kakashi working for Root under their rules. Perhaps Rin was Root, and Kakashi was Anbu. And Rin asked Kakashi to help on a mission on Danzou's orders. That's the only way I think this theory could work. Otherwise they were both chosen for their unique abilities because the situation called for it.
Sorry for the long post.