This post was very well articulated and raised some very interesting points, especially regarding the connections between knowledge, free will and the boys' views on that. The boys regularly are forced to make decisions based on incomplete knowledge and there in lies the source of most of their mistakes. See pretty much all of season 4 for examples. In the episode with Jesse, Castiel accuses Sam of having used his free will for evil, but the truth is, he lacked all the facts and was deliberately misled not only by Ruby, but by the angels as well. Sam, it seems to me, has repeatedly expressed the idea that evil was something that would come and take him over (see House of the Holy and Playthings) rather than a series of progressive choices. I wonder if this attitude stems from the fact that, for most of Sam's life, all his choices had been made for him, generally by John. He was kept in the dark about the facts and his range of options and thus has a very strange relationship with choice. Dean, on the other hand, for all the good soldier talk, actually knew the score and made his choices, and maybe that's why he realizes that it is what you chose to do that makes you who you are in a way that Sam generally doesn't.