Fred, we have seen it time and time again. If you outright hand a young player a job, he is more likely to fail. If you tell him he has to earn it, he works harder for it. All of your examples were players that needed to compete for spots at one time or another.
Middlebrooks was handed the job and failed. Pedroia -- one of your examples -- had to fight out Alex Cora in 2007. Jed Lowrie had to beat out Scutaro.Doubront had to beat out a mediocre group of guys like Aaron Cook, but he did end up earning the spot. He was handed the spot last year, and showed up to camp way overweight. Iglesias knew he was on the bubble so he played hard at both SS and 3B to stay relevant. Lester grabbed onto his rotation spot and never let go... but he competed with Beckett for that "#1 starter" spot for most of his career. Ellsbury? Coco crisp.
There is nothing wrong with competition. Handing players a spot is ALWAYS a terrible idea, with overpaid veterans AND young players. Get as much talent as possible, and let the best player get the opportunities. That is how the game should be played.