The problem for Christians is that they can't believe that a good and just god would just dump people in Hell for something that isn't under their control. So they believe (and must believe if they want to keep their Christian theology consistent with their 21st century Enlightenment moral beliefs) that atheists really, secretly, do believe that God exists, but deliberately pretend that they don't believe so they can continue to live their debauched lives.
Calvinists are a bit less illogical. They don't think that there is any choice whatsoever on the part of the person. All people are damned and deserve to go to Hell, but God, for whatever reason he has, has decided that a few will be saved. The few that will be saved will be moved by the Holy Spirit (and this will be irresistable) to become saved.
Actually, if their god makes better pancakes, I'm totally switching sides. --
Charley the Australopithecine