First off, there is no Hell – not in the modern sense of the term anyway. Jesus promised eternal life only for his followers. Everyone else just dies and their souls are destroyed. End of story [Romans 6:23].
The fiery furnace is merely symbolic of utter destruction. No souls are kept alive forever in a state of perpetual torment. That imagery comes to us thanks to Dante’s Inferno and prior to that, from Tartarus of Greek mythology. It is to be found nowhere in the Bible*.
It is impossible for the human mind to comprehend true nothingness. Even that “nothingness” we try to imagine is, in fact, something. At best, we can imagine a situation like being in a womb or a sensory deprivation tank. But even then we are fully aware. Our minds are active. Total oblivion is a foreign concept. That is why we must imagine death as being something rather than nothing.
On the other hand, our minds are fully adept at visualizing unpleasant scenarios. Perhaps it is a survival mechanism passed down from our ancestors. Whatever the case, it is infinitely easier for us to imagine an unpleasant place where our awarenesses somehow continue rather than nothing at all.
“Hell” has therefore become the “bad” place where we live forever as opposed to Heaven, the “good” place where we live forever. The former couldn’t be further from the truth.
Some people die and don’t go to Heaven. But that doesn’t mean they are someplace else. It means that they are simply gone. But most atheists believe that already. So in at least one sense, they are right.
And as for Heaven, why would a non-Christian want to spend an eternity in a Christian Heaven anyway? Most non-Christians I know can barely stand being in the presence of Christians praising God for fifteen minutes let alone a trillion years. To them, perhaps, such a place would truly be Hell. Oblivion, then, would be the ultimate loving kindness.
*[Although there are several places in the Bible that speak of eternal punishment or damnation it also speaks frequently of the soul’s utter destruction. To avoid contradiction, this can only mean that the punishment is death and it lasts for eternity. The destruction process is usually described in unpleasant terms but death is rarely pleasant.]