I don't believe in Hell. Several years ago I decided to fully accept the preterist theory (short version: everything in the Bible has already happened); this has led me to universalism - everyone goes to heaven. I've held this belief for quite a while now.
I just changed it - somewhat. I suddenly believe in Hell, a place of such misery and torture that people can't really imagine it. A horrifying place. I also believe I'm in it right now, I just found a tiny bit which is somewhat less horrible. (I try not to make too many waves so I don't get moved to a more horrible part.)
This movie is why I think so - Johnny Got His Gun. It made me realize that politicians and soldiers are, if not the Devil, then something very close to it. They do their best to make other people's lives and homes a Hell. Hiroshima and Nagasaki might have been the clearest example, but read this description of the carpet bombing of Tokyo from Wikipedia:
On March 9 and 10 1945, B-29 Superfortresses were directed to bomb the most heavily populated civilian sectors of Tokyo. In just 2 days of bombing, over 100,000 of the population had burned to death from a heavy bombardment of incendiary bombs. Another 100,000 were left homeless.
We're in Hell. I now understand why some people commit suicide - they just discovered this, and can't handle it.
As for the rest of us - it's our job to make it better... though it's hard to be optimistic when I see how many people around me still worship the Devil.
Edit: For another horrible example, North Korea's death camps.