I've lost count of the number of times I've been told that I will "burn in hell" for not believing that Jesus was divine. I actually believe that there's a possibility he existed historically, but that he was a very human religious teacher rather than a divine god creature.
The trouble with this statement, "burn in hell", is that it's inaccurate. The main reference to lakes of fire and the fiery abyss are in Revelations - which has more credibility as a political treatise that as an eschatological work, and wasn't written until late in the 1st Century (Irenaeus states around 95AD). Other references are scattered through the New Testament. However, the modern Christian view of a fiery Hell comes from the Greco-Roman vision of Tartarus, and is not the traditional Jewish view which Jesus would have recognised. It would be a good guess that this vision of Hell came in to play once Paul and other Hellenised Jews began to form the Christ movement in the decades following Jesus' death. The Greek learning of the Biblical authors colouring their imagery, rather than the Hebraic imagery of the earlier books.
Traditional Jewish belief is that of a purgatory state which can last up to a year (hence the saying of Kaddish and sitting shiva). You reflect on the sins of your life and then move on to heaven (rest) or to sheol ("death" or "the grave" rather than hell). Non-believers aren't automatically condemned as long as they follow a righteous life (preferably by following the seven Noahide laws that apply to all humankind). On the resurrection, the righteous dead will live again in bodily form on Earth (the "Kingdom of God" described by Jesus). This earthly Kingdom of God would be ruled, in God's name, by the messiah - the descendent of David. This is what Jesus' disciples believed Jesus to be, and was the throne Jesus was claiming.
In the New Testament, this vision of an earthly Kingdom is again born out again and again in Jesus' teachings - as recorded in the gospels. The three synoptic gospels, and even the Acts of the Apostles and Paul's letters, all refer to an earthly Kingdom of God which Jesus will return to establish. These writings are all 1st Century. When this didn't occur, the message of a spiritual kingdom began to circulate. Now, this is all we have. Because of this later move (late 1st Century and 2nd Century) toward a spiritual kingdom, the vision of heaven and hell is firmly Greco-Roman rather than Jewish. Modern Christians basically believe in Elysium and Tartarus. If you're Catholic, there's also Hades thrown in to the mix - which at least is comparable with the Jewish purgatory concept.
"The wages for sin is death" says Romans 6:23. As this is what most secular atheists believe anyway, it's not very effective to threaten them with it. The denial of the sight of God, a god that an atheist doesn't believe in, isn't much of a threat either. So why bother? The lack of a fiery hell to scare people with might force Christians to actually think about their religion. A rethink of the message being given in the Bible may also make some of the eschatologically focussed Christians reconsider the environment. God's Kingdom is meant to be here on Earth - build it, and He may come (to paraphrase Field of Dreams).