Hellfire preaching stirs up a lot of different ideas in the minds of people. For non-Christians I think that what comes to thought is the idea of someone pointing their finger at them saying "you're going to hell". Maybe it's from an experience they have had; maybe it's just an assumption. Either way most are against it.
And for many Christians, I think what comes to mind is almost the same - we tend to think of a sermon meant toward non-Christians. Regardless of the detail or brevity of the message; we tend to kind of close our ears and say "this isn't meant for me".
Well I ask; if you know the severity of hell - the torment, the anguish, the pain, the "fire and brimstone" - the eternity of it etc. Would you condemn anyone to that? Is there anyone that you would actually wish to go there? I imagine none of us desire anyone to go there - but for those who are headed to hell, if we don't warn them - are we not condemning them to that fate?
Hellfire preaching should not be limited to non-Christians. We need to be reminded of every detail of it's awfulness. And we should have our compassion cultivated so much by it, that it compels us to do all that we can to keep souls from going there.