I don’t personally experience their level of discomfort around people who believe in the existence of Hell in the same sickening way, but I find this an entirely understandable reaction.
It seems too obvious to even mention, but that’s almost never universal, so it’s worth spelling out: Hell, as generally described or conceived as a place of everlasting suffering, is the most evil idea that is possible to exist.
There are various other interpretations of what Hell is – “an absence of God” or what-have-you – which may or may not be more theologically rigorous than the colloquial usage. But the lasting image in many people’s minds is pretty much congruent with all those Renaissance paintings of lakes of fire filled with sinners. If you go there, you will be tormented without end. And whatever disagreement there is on what it takes to get sent there, this happens to a non-zero number of eternal souls.
Seriously, if you can come up with something even hypothetically more evil than that, leave a comment or something, I’d be fascinated.
So while there’s something horrifying about wishing that somebody would suffer such a fate, there’s an extra layer of grotesquery in accepting that such a self-evidently evil thing could be allowed to exist by a god who claims to love us, and who somehow still deserves our love in return. That it’s a sad necessity, or part of some great divine plan we’re not privy to, and not proof that this god is an abominable tyrant who we must never stop railing against.
All that said… I think the saving grace here is that most people just haven’t thought it through.
I can’t know what’s going on in other people’s brains, but I strongly suspect that many of those who profess a belief in Hell haven’t consciously, deliberately, formed a mental model of all the implications of that belief and truly accepted them. Far more likely that many of them are replacing the question with a different one, and answering that instead.
Rather than “What is an appropriate and reasonable punishment for people who do wrong?” they’re responding to something about how important it is to them to defend the integrity of their tribe, and how strong is the hate they feel toward the out-group. The feeling of enmity toward the other is interpreted as a wish for some non-specific ills to fall on said other, but in practice, they’re probably not imagining anything more appalling or painful happening to them than, say, death. (This is the same misunderstanding of scale as is often seen in the dust-speck issue, where people read “3^^^3” and think “billions, probably”.)
So, yeah. If you believe in Hell, then potentially we could still be friends, although it’s not exactly a great start. If you believe in Hell and we’re already friends, well, just know that I disagree with you on this even more than I disagree with you on politics, and we both know how out-of-sync I am on that front.