"If everyone demanded peace instead of another television set, then there'd be peace." --John Lennon

If you could make everyone in the world read one book, watch one film, or have one experience, what would you have them read/watch/experience?

This is too tough a question for me to answer without more thought, but I would say the reading that has, standing alone, changed my life more than any other was Leo Tolstoy's What is to be Done?
I would certainly recommend this to absolutely everyone and anyone. He does not only present issues that have transcended generations and cultures, but presents to us the question of why we say we are concerned with these issues while we live the way we do. Still, I don't think this is my concrete answer to your question. I will have to think about that.