Thank You For Smoking
I'm a lifelong non-smoker. I lecture my friends who do smoke about why they need to stop. I've voted for just about any anti-smoking legeslation that has been on the ballot, even if it clashes with my libertarian values.
But Thank You For Smoking is the best movie I have seen in years. The movie is an hour and 27 minutes, and it will make you think for a long while afterwards.
I don't want to spoil it for you. For more information, here's a review from Roger Ebert.