If God is so merciful then why does He allow people to go to Hell?

Early this afternoon I went to Barnes and Noble with my work partner, Michelle. We spent a couple of hours there and during that time I picked up a book from the Christian Inspiration section and read it. (yeah, pretty much the whole thing excluding the authors notes and stuff in the back of the book.) It was called  Nine Days in Heaven. I've read 90 Minutes in Heaven and 23 Minutes in Hell, and though the books were an interesting look at Heaven and Hell neither of them really resonated with me, so when I saw this title it didn't really strike much interest in me, but I did want to see if it was any different from the other two books, so I read the back cover and found myself intensely curious.

This was the descriptions for those who want to know what struck my curiosity: "Marietta Davis fell into a trance at age twenty-five that lasted nine days. She experienced a vision that made her a legend. When she finally regained consciousness she described with extraordinary graphic detail scenes of how angels had conducted her spirit to heaven and hell. Marietta made it clear that her vision was given for her to tell the world so people could prepare for the afterlife."

While I was reading I was given many things to think about, but I think none of them came so strongly as the idea of a merciful God sending people to Hell.  We can give the tired old arguments (though very valid) of sin and holiness and the fact that sin and holiness cannot dwell together, but I'm not sure those answers can really satisfy the question when it's centered around mercy. Anyway, as I was reading it dawned on me that the fact that God does allow people to go to Hell proves His mercy, because perhaps Hell itself, though it is a place of judgement, is God still showing mercy on those who have been judged and found guilty.

I know if anyone is reading this they're probably writing me off as a complete idiot right now, but hear me out.

In this book, Marrietta had visited/seen visions of both Heaven and Hell (and keep in mind that she is not seeing them as a Christian). Whether she really visited or just had a vision, or even a dream doesn't make a difference to me so we're not even going to question it because I don't think it changes what I realized.   Anyway, she see's Heaven and it's wonder's first and then she see's Hell second and the incredible contrast it was to Heaven's glory.

It was very descriptive, it showed hell as a place where people are given over to their evil desires and as they pursue them they ultimately become a slave to their desires and find them unquenchable and thus live in despair. They live with the knowledge that they had turned their backs on God and crumble in the despair that there was no hope of redemption left for them. In seeing Marrietta in Hell and knowing she didn't belong there (yet) because she was not dead but still had a shot at redemption drove them further into the agony and despair they were suffering. They were sinful and suffering, and their sinfulness bred more sin and suffering, like an endless cycle they couldn't escape. And this was only the surface of Hell.

After seeing Hell, she saw Heaven again where she heard the melody and unity of worship to God in love and found it so beautiful she longed to join in but as she tried she found that she could not align herself to the Melody and the more she tried the more she found herself in her own Hell because she realized that she was unfit for Heaven.  The realization drove her mad because she realized that when she tried to join in, she was ruining the song as she did not possess the holiness or the love that caused the angels to sing as one this beautiful song of worship.  Her sinfulness ruined it's purity.

The idea was presented that when people die they are ushered to the place where there are souls like themselves, so an evil soul that resisted God was ushered to Hell, a soul cleansed and redeemed by Christ was ushered to Heaven. I thought this was an interesting idea in light of the things she saw in Heaven and Hell. Even Isaiah, when he was in the midst of perfect holiness and purity could only despair of His sinfulness and how he was unfit to be there.

It seems that if sinful people who have not been freed from the bondage of sin were allowed into heaven, they would contaminate heaven, no doubt, but I feel that it might be worse for them than Hell itself. In Hell, they may be recieving the justice due to them, but in Heaven they would be laid bare, exposed, not covered by God's grace as they had never accepted it. They would have a constant reminder that they are unfit for God's Kingdom, that they could never truly be a part of it, that they could never take part in the beauty, lest they ruin it. To me that is far worse than any Hell I can imagine.  It reminds me of 2 Peter 2:21 that says It would be better if they had never known the right way to live than to know it and then reject the holy commandments that were given to them.  (NLT)
Even though I know this verse it talking about people who turn their backs on Salvation, it seems to fit that it would be less despairing for a person to have never seen Heaven and suffer in Hell than it would be for a person to see Heaven and find themselves condemned. That's why I speculate that Hell, though it's purpose remains, could still be an act of mercy on God's part.

I acknowledge that I could be wrong. But it was intersting to think about.