Christians: do you really believe all non religious people will go to hell once they die?

No, I don't. I don't believe in a Hell of suffering and torment; from what I can tell, in the original message Hell was just the place where the dead lived (Sheol) or more accurately, slept, aware of nothing. Even if the Hell of suffering and torment is the correct interpretation, I don't believe that disbelief in God will get you there. I believe that in order to go there you must deliberately reject God's message. People who haven't had sufficient evidence presented to them to believe, but are overall good people, will get to Heaven. People who have seen the evidence, but rejected it because their minds were closed, will not get to Heaven, and will either sleep eternally or suffer torture, whichever the truth happens to be.