I think Dean would tell himself, starting as young as he needed to (six, seven, etc.) that whatever he needed to do to ensure Sammy was taken care of...that's what had to be done. "Take care of Sammy" is his catch-phrase -- he says it himself, in AHBL2. "I had one job" and "Dad didn't even have to tell me". And we know from things revealed in the course of the seasons so far, Dean's identity comes from how well he takes care of his family. I don't think he would even think there was a choice; Sammy needs something, Dean does whatever's necessary to get it.

Kind of heart-breaking, isn't it?