I've always been annoyed by the "fire and brimstone" preachers and Christians. Not because I necessarily disagreed with them, but because of what they implied. Too many of them were almost trying to scare people into The Kingdom. "If you don't come to Christ, these horrible things are going to happen to you." Not only is this not appealing to most people, it comes from a very flawed way of understanding the choice that we make when we accept Christ.
When we accept Christ as our Lord and Savior, we are actively choosing Him. We are not coming to Him as a last ditch effort to avoid something unpleasant (Hell). Since we are relational creatures, we don't just pick the lesser of the discomforts, we make particular choices because we believe that they are set apart from the other options in a very distinct way.
On the "fire and brimstone" model, people would be simply choosing to avoid Hell rather than choosing to be with God (Heaven). There is a difference. Kind of like choosing between two painful options- you would pick the less painful, not because you really desired it, but because it was less painful.
If we were simply avoiding Hell, then we would not really be actively choosing anything else, just not Hell (anything but Hell). I would expect to see these types of sermons more in universalistic churches, simply because they allow many ways to avoid Hell. Their "gospel" "provides" "ways" to avoid Hell, but not actively choose Christ.
Now, I am not going to say that these sermons are not needed; they are. But they are targeted towards the wrong people. These sermons should be targeted to the Body of Christ. "Look at what will happen, if you do not go preach the Gospel of Christ." Of course, this assumes that humanity has intrinsic value, but that is another topic (see my post "Martin Luther King Jr. vs. Evolution"). I will grant that this may seem that I am promoting evangelism based on the Christian's fear of what will happen to the lost. However, the true Christian who has a deep relationship with Christ and loves others, will understand the value that another having a relationship with Christ will have for the other person's life (now and forever).
As Christians, we should evangelize because we desire that others have the same joy and security that we possess. The "fire and brimstone" sermons for the Christians should serve to "light a fire" (no pun intended) under those who's passion for Christ is not burning as hot as it once was (and/or should be). To add a little more balance, sermons should also include convicting messages about growing closer to Christ. The more we know Christ, the more we know why others should know Him too.
Just like if I find a product that has high value, I recommend it and help people get it, because I want them to benefit in the same way that I have. If we know why others should know Christ, we desire to share Him with others. In the case of the product recommendation, the consequences of not using it are typically trivial. However, that is not so if the Christian worldview is true. If we believe that the Christian worldview is true, then we must accept that the consequences of not choosing Christ are not trivial either.
But how can we balance our focus between the love of Christ and the fear of the consequences? We tend to gravitate toward one approach or the other in our preaching and our evangelizing (and even our own personal beliefs). The answer comes in understanding why we should choose Christ at all. The Godhead is a morally perfect, personal being who desires a relationship with man. In order for man to have this relationship, he must also be perfect, but he is not (you make one morally wrong decision, and perfection is out of the question). However, Jesus loved us and desired that relationship with us so much that He provided us a way to have that relationship with Him. But, we must actively choose the gift; if you do not desire the gift, you won't get the gift.
One must understand that he is a morally broken being, there is a morally perfect Being who desires a relationship with him, he cannot have this relationship without perfection, the morally perfect Being provided a way to moral perfection, and finally the person must accept the way provided. If one does not accept the way provided, his claim to desire a relationship with the morally perfect Being is a lie. God created you; He knows everything about you- including your true desires.
Jesus Christ paid the penalty for our moral imperfection when he suffered on the cross. He was the sacrifice that the Father required for our transgressions. If we truly desire a relationship with a morally perfect God, we must accept the gift that Christ offers to us that will give us that relationship. If we don't accept the gift, He will not give it to us. If we accept the Gift, we gain an eternal relationship with God (avoiding Hell's fire is just a perk of that eternal relationship with God).
If you don't desire something, why complain that you won't get it? And if you don't believe that Christianity is true anyway, why are you so concerned with the doctrine of Hell?