From a relatively outside view (my upbringing was semi-secular Jewish), belief in heaven and hell is really strong stuff for some proportion of people-- I'm not sure how high the proportion is, but people can make themselves acutely miserable from fear of hell and/or fear of not getting into heaven.
To be fair to Mormons, they don't have the concept of an eternal hell like most Christian fundamentalists. There is something called "outer darkness", but you'd have to work really, really hard to get there--like, harder than Hitler.
From the final chapter of his new book Cowards, titled "Adapt or Die: The Coming Intelligence Explosion."
The citations for the chapter include: