If hell exists -- and I know that's a big "if" by the estimation of some -- it is entirely reasonable to speak and act as if it is the gravest danger facing anyone. It would certainly be more dangerous than bodily death, if Jesus' logic is to have any influence.
The principle at work here is similar to that at work in atheist Penn Jillette's well-spread word on Christian proselytization. Jillette does not believe hell exists; he doesn't even believe God exists. But he says if you believe it does, it is not hateful to warn him about it: it's hateful not to. This is called being logical. Jillette uses the illustration of a speeding bus. If he's standing in its way and doesn't see it coming, the loving thing to do is to push him out of its way. He then asks, "How much do you have to hate someone not to proselytize?"
So it may make one uncomfortable when others get upset when other Christians deny the existence of hell. But doesn't it make sense? Logically speaking, if hell does exist, it makes perfect sense to get angry when other self-professing Christians say it doesn't. Or that it's not as bad as we've made it out to be. Many critical of those who reacted quite vocally to the most recent questioning of hell, I dare say, would not be critical of those angry about the denial of cigarette smoker's risk of lung cancer. If I posted a blog angry about somebody's denial of racism, I would get Amen's.
But we're talking about hell here. It's not hateful to get angry about the downplaying of hell. Certainly we should talk about hell in gracious ways -- which is to say, we should not be "bad news" people but "good news" people, so we should not preach hell the way some of our fundamentalist forebears did, as if hell was the only reality. We ought to say it is real and it is a danger to those apart from Christ, and then we ought to hold out Christ as the glorious, wonderful, hell-proof hope.
Preaching hell in the context of the gospel is not hate. And getting angry about the denial of hell is not bloodthirst: it is what logical people do when someone says that giant waterfall your canoe is heading for isn't really there. It is an anger born not of hate, but love.
"If there be really a hell of such dreadful, and neverending torments, as is generally supposed, that multitudes are in great danger of, and that the bigger part of men in Christian countries do actually from generation to generation fall into, for want of a sense of the terribleness of it, and their danger of it, and so for want of taking due care to avoid it; then why is it not proper for those that have the care of souls, to take great pains to make men sensible of it? Why should they not be told as much of the truth as can be?
"If I am in danger of going to hell, I should be glad to know as much as possibly I can of the dreadfulness of it: if I am very prone to neglect due care to avoid it, he does me the best kindness, that does most to represent to me the truth of the case, that sets forth my misery and danger in the liveliest manner."
--Jonathan Edwards, Distinguishing Marks of a Work of the Spirit of God