My biggest problem with the idea of Obi-Wan telling Luke exactly what happened to Anakin in the very beginning is Luke's reaction. He just stares at Old Ben dumbfounded as he reveals that his father's not really dead, but an agent of evil responsible for the extermination of the Jedi order. And oh, by the way, here's his lightsaber: you should have it. I appreciate what we're trying to do here with Obi-Wan's character, but it's just not going go smoothly, and will create more problems than it solves. I had hoped at the end of RotS that Yoda would tell Obi-Wan, "Tell the children of their true parantage we must not, Obi-Wan. Better they believe a different truth than the terrible one that is. Confuse them it will, and lead them on a path to darkness. Until the time is right, unaware they must be." Or something along those lines to get the point across that Yoda and Obi-Wan had their reasons for keeping Anakin=Vader a secret, and planned to reveal it to them at the proper time. Seriously, if you were Obi-Wan, and you want Luke to join you, but he asks about his father. What do you tell him, that his old man was a good friend and student of his before turning evil, betraying the Jedi, and become the second evilist man in the galaxy? Yeah, that would go over well.