[Hells Sniper]

The thing behind humanity and the Librarian is that she saw them fit to take over the Mantle after the Forerunners. Because by the time she was taking interest in them, it was after they were reverted to the cavemen ages and the Flood-Forerunner War was taking place. She knew the Forerunners would and could never return, and she saw humanity as the next race to take over the Mantle of Responsibility. It also helped that humanity figured out a flood antidote prior to the Human-Forerunner War, the antidote was unfortunately lost and thus why the Forerunners basically lost the war. As for the Master Chief thing, I think what you have to keep in mind is that this Spartan saved humanity...twice. He was a soldier, yes, and that's completely touched upon in the end of the game, but he was a soldier who understood the enemy and was given valuable information on the Didact's next move, which Del Rio just dismissed in a "You're crazy" rant. Del Rio was relieved of his command because he didn't take the information that one of the most valuable soldiers humanity ever had into consideration. If he did, the attack on New Phoenix could have been prevented. Del Rio was a very by the books guy, but even FLEETCOM can understand the necessity to go off the books to do the necessary.