When has an atheist ever threatened a Christian with a fate worse than our worst fears?

It all depends on if there really is something to warn somebody against. If my friend lets her 3-year old in my backyard and there is a pool, I am obligated to warn her about it. If I do not believe that pool exists, that does not negate my responsibility if the child drowns. If hell exists, Christians are under an obligation to warn people about it. And if it exists, atheists are not tolerant people simply because they refused to acknowledge a very real danger.