I found the theme of free will quite intrigueing in this episode. I am not even sure a tumor really exists in Ben, or if it is a scripted situation created to test Jack's moral compass.

When Ben Speaks to Jack after the funeral he tells him point blank what their agenda is: "we had a plan to break you" and "to lead you to believe you were CHOOSING to do whatever we asked you to do."
Jack:"You want me to save your life."
Ben: "No, I want you to WANT to save my life." (there is a difference)
He then equated Jack's falling from the sky as an act of God. Which is a powerful manipulation.

Later Juliet speaking to Jack (while opposing messages are being held up on the screen)
"You probably feel like you don't have a choice." "Free will is all we've really got."
She is saying these things with her mouth, but the video tape is asking him to murder Ben because he is a dangerous bad liar that everyone is afraid of.

She tells Jack that the movie she has brought him is "To Kill a Mockingbird" The theme of this story found is a teachers guide: To Kill a Mockingbird is an exploration of human morality, and presents a constant conversation regarding the inherent goodness or evilness of people. Atticus, father of Scout and Jem, also plays the role of teacher, for his children and his town. Atticus believes that people usually contain aspects of both good and evil, but that good will usually prevail."

I believe that free will was also a prevalent theme with Eko's storyline. Two brothers were born into the same violent world. One chose a path of humility and peace. The other chose the same violent path as those who nearly murdered his young brother. He stated that he did not feel he had any other choice, but clearly he did.