This is where I like to point out the second half of John 3:16 says that anyone who doubts Jesus goes to hell.
1) The second half of John 3:16 says "whoever believes in him shall not perish but have eternal life", not "whoever doubts in him shall not live but be eternally damned." These are different concepts, so I don't believe your characterization of this verse is accurate.
2) CS Lewis has a chapter on hell in The Problem with Pain. Not sure it was exactly orthodox Christian thought, but interesting nonetheless. He essentially stated the being banished to hell meant destruction, instead of eternal torment.
3) The "fires of hell" may not mean literal fire, but could mean metaphorical. As Belgiansocialist pointed out, many theologians have referred to the torment of hell as being deprived from God's presence, as opposed to a medieval torture chamber. It would seem to be more like being forever separated from your closest family member, not physical pain as much as intense feelings of loss and regret.
4) As the Christian God is often described as a just God, it is not about having a moment of doubt and being punished for it for all time. Those condemned to hell are confirmed as evil due to their hatred of God.