But, even then, Madara is still not lying in a way that encourages trust between he and Sasuke. He is doing it in a way that, while it may destabilize Sasuke, he is only increasing the gap between him. Because:
A. Sasuke believes Madara that Itachi was good and is overcome with guilt. He recognizes Madara as the major reason for all of his suffering and vows to destroy him.
B. Sasuke doesn't believe Madara, and the author just wasted several chapters over a random lie that has no meaning.
It is very easy to think of possibilities. Is it possible that Madara is lying? Yes. Does that make sense? No.
Why? Because it has clearly been set up from the start. You are a consumer, correct? As a consumer, are you going to be happy if the entire edition you just bought is one giant lie? No. You won't. It doesn't strengthen the plot if Madara is lying. It shakes it up and destroys a ton of character development for Sasuke and Itachi, and weaken's their story as well.
However, if Madara is telling the truth, Sasuke now has:
-A reason to still be in the manga, be it for or against Madara and/or Konoha.
-A ton of character development, as he will be forced to question every thought he has had about his brother for years.
-A ton of answers for previous questions.
If Madara is lying, we have:
-I guess a potential arc where Sasuke joins Akatsuki, although that just sounds boring.
-No character development for Itachi or Sasuke.
-No questions to answers.
-No reason for several chapters to be dedicated to a "fake history" that has been built up over the course of the series.
While, character-wise, there may be some reason for Madara to lie (although this is completely unfounded by anything stated in the manga), there just isn't any point for it design-wise. The story is stronger if it is the truth. Just as the story was stronger because Jiraiya died instead of escaping, Orochimaru is gone for good so we can move on to new villains, Tsunade becomes the Hokage, Naruto learns to advance the Rasengan, Sakura becomes a medical ninja, blah, blah, blah.
No author will intentionally weaken their story.
And there is no proof for your basis that "Madara is always lying." Actually, Madara is the only one consistently up-front about everything.
Yes I killed your family. Yes, I was beaten by the stupid, first Hokage (who I unfortunately admired). Yes, I controlled the Kyuubi. Yes, I created Akatsuki.
The only "lie" is him pretending to be an idiot so that he can spy on Akatsuki easily while Pein secretly reports to him.
Seriously, either create an argument from story aspects or design standpoints.
And saying that Sarutobi wanted peace overall means NOTHING. Naruto wants peace as well, but it doesn't stop him from killing a rival Shinobi if he has to.
Sarutobi led Konoha through a war so that it came out strong, and assigned assasination missions to shinobi everyday. He runs off into battle with the rest of them. He tries to rip out Orochimaru's soul.
He was a peace-lover, yes, but one of the major themes of Naruto is that the children are the future that will see past our own foolishness. Sarutobi may have loved peace, but he was still a warrior from a rough past. He WOULD have killed the Uchiha clan if necessary. This is a man that was willing to send a group of thirteen year olds into an enemy infested area during a war (Kakashi Gaiden). He understood a balance system where some evil was necessary for the greater good.
Which brings more peace? The Uchiha clan destroys/takes over Konoha during a civil war costing many lives. The Uchihas are quietly dispatched in one night and the people grieve, but move on.
It is easy to see. It is the same way Danzou is an "enemy" now. If the Fifth got proof that he was planning something terrible, he would be killed instantly and Root disbanded.
Konoha protects Konoha before it protects the individual. The Hokage is a leader because he is recognized as being the best man for the job. If the elders didn't think that he was doing it correctly, I am sure that they could do away with him.
Why else would Tsunade agree to their demands, if she could just say, "I'm Hokage, I do what I want,"?