Well, Sasuke was able to awaken his Mangekyo because of Tobi. Pretty sure if Tobi didn't tell him what Itachi did, Sasuke wouldn't have changed his feelings or felt the way he did about Itachi's death and his role in it.
But simply because Obito came in later and had an effect doesn't mean that Sasuke wouldn't have awoken it without him interfering. If someone as smart as Itachi believed it would work, then there's a good chance that it would have. In either case, Sasuke would still have had feeling of regret and such.
Why would he have had strong feelings of regret for killing someone who killed his family for fun? I don't think Itachi planned on unlocking Sasuke's MS with his death, but he probably thought Sharingan Sasuke could be enough, especially with Naruto. The only reason Sasuke felt any remorse or regret for what he did to Itachi was because Tobi told him what happened. Those feelings are what likely awakened his Mangekyo.
Sasuke seem quite depressed and regretful afterward, before Obito began telling his story. And Obito attributed the entire reason for Itachi fighting Sasuke to that reason, to awaken his MS. When you get down to it, there wasn't much reason outside of that for Itachi to even fight Sasuke, except perhaps to get rid of Orochimaru.
Then why would he encourage Sasuke to get his MS before their confrontation? Tobi's words aren't facts, they're statements, what he thinks. He could have been wrong.
I'm not sure if Sasuke was depressed at the fact that he killed Itachi, but likely wondering where to go after killing the person he dedicated his life to killing. Sasuke didn't look depressed before he fainted, he was laughing if I recall. It wasn't until he woke up in Tobi's lair that he didn't look so happy, but once again that could be attributed to Sasuke wondering what to do or where to go since his goal that he dedicated his life for was finally achieved.
I'm not saying that was the original plan, simply what Itachi decided after left Naruto and joined Orochimaru. He obviously had to change his plans to account for Sasuke's decisions. Sasuke only coughed and hyperventilated, no laughing. Anyway, being depressed because he no longer had something to direct him would still tie into a strong emotion. Plus there was also Itachi's last remark to him.
Konoha would oblige because Itachi was not only their double-agent, but keeping him happy prevented him from spilling the village's secrets to the other villages. Itachi would risk it because it's about Sasuke, and for him Itachi would take any risk. Don't think Zetsu would care either way since it doesn't endanger their plans, and anything he told Itachi would likely be verified.
But if someone catches him and Konoha getting along, the whole plan could backfire. I doubt Itachi would take that kind of risk, especially when Konoha is supposed to hate Itachi and call him a traitor. The only thing keepin gItachi was happy was the safety of Sasuke, otherwise as long as Konoha was safe I doubt he cared about being happy.
It'd endanger Itachi's plans, and it did until he was Edo Tensei'd. Tobi knowing everything allowed him to tell Sasuke what happened.
Itachi showed he could easily enter the village and remains hidden til he wanted to, so he shouldn't have had much trouble sneaking in and reporting directly to Danzo and co. He must have had the means, given that he was reporting information to the higher-ups before his death. And knowing what occurred with Sasuke and Konoha's intentions would be keeping with his safety.
It didn't endanger Zetsu and Obito's plan though. If anything, it was in their favor, hastening Itachi's eventual death and allowing Obito to finally act against Konoha and make a grab for Sasuke.
abolishing the ninja system is not the answer to peace. look at the real world, which Kishimoto tries to mirror into the Naruto/ninja series. It will most likely end in a similar way DBZ ended, a tournament of some kind, perhaps a unified village with kages as leaders of different areas aka world government.
this will ensure the longevity of the series, especially game developers who are thinking of making an mmorpg of naruto, action games, whatever, you name it!