H/T Banksy. Major caveat - I haven't yet read the book, so this could be completely off-base, and I reserve the right to amend it if it needs to be!
First point: I became an atheist at the age of about 14 after a long conversation with a school friend about Gandhi, and whether he was going to hell or not. So I understand and accept the broad point being made, that our understandings of hell are often sub-Christian at best. However...
There is a way of understanding the heaven and hell conundrum called 'universalism', by which is meant the idea that, in the end, nobody escapes salvation. It was first proposed - I believe - by Origen in the second century. It was also fairly swiftly condemned as heretical - and I think it is right that universalism is condemned as heretical.
A Wittgenstein quote on the subject (from memory): "Of course it was condemned as heresy. If what we do now makes no difference in the end then all the seriousness of life is done away with." The seriousness of life - the idea that what we do makes a difference, for good or for evil. Without that dimension to life - what Wittgenstein called 'depth' in many other places - then something essential to our humanity is lost - after all, if nothing that we do makes any difference, then what is the point of all this painful drama?
My worry about universalism is that it is a form of political correctness applied to God - heaven is a multicultural wonderland where everyone is righteously right-on.
I hope Bell isn't going to come out as a universalist. I've rather liked his stuff hitherto.
For what it's worth, some of the best stuff I've read about hell in recent years has come from the wonderful writings of James Alison, and this sums it up:
"The commonly held understanding of hell remains trapped within the apocalyptic imagination, that is, it is the result of a violent separation between the good and the evil worked by a vengeful god. It seems to me that if hell is understood thus, we have quite simply not understood the Christian faith..."There is no wrath in God...