You're all incorrect. The reason he demanded the demonstraition as a show of good faith, as well as having a safe key. Obi to knows damn well Kabuto would try to off him when both sides of the destroy each other. Having Kabuto do it in front of his eyes, he wouldn't be decieved. His goal isn't to get Rin back. He could have sought Orochimaru for the exact same thing, MANY years prior. Obi to knows it's flaws, and the one weakness.