I wish they had cast someone, anyone else, for the role, but not for any of the reasons given here. I personally, couldn't get past the fact that Mortensen is a dead ringer for my cousin, right down to the creases around his eyes. Each time they showed a close up of him in the movie, I was shaken out of my suspension of disbelief, while my brain processed the fact that that "this is really weird, this is not the kid with whom I spent my childhood". It was brief, but annoying enough to disrupt the continuity of the film for me.