What's so hard to believe about Hell? Tell me if the following scenario sounds logical to you.
Once there was an archangel named Lucifer. The role God intended for him to carry out was to be a good and mighty servant of God. But Lucifer rebelled against his God-given place in nature, so he and his followers had to be cast out of Heaven. Now God hates to destroy spirits, so instead he created a spiritual realm suitable for those spirits who are in total rebellion against God's will. This realm is called Hell. So Lucifer and his host of fallen angels were cast into Hell, and they are now Satan, the enemy, and his horde of demons.
Cut to humanity. Humanity was made to eternally live in the flesh and to serve God on Earth. But humans enter into rebellion against God as well. It's not a total rebellion, like the demons', and they do repent of it afterwards, but all the same from that moment on humans have a hard time with not trying to claim some sort of independence from God. With humanity in rebellion against God, the miraculous forces which protected their bodies from the natural process of decay are taken away, and the death of the body becomes part of mankind's destiny. When man dies, he becomes pure spirit, and there are ultimately only two realms where spirits can go: Heaven is for those who wish to submit to God's will, and Hell is for those who do not.
So Hell is a place for both dead humans who are in rebellion against God, and for demons. And demons really hate humans. Thus, demons torture damned humans. God does not protect damned humans because they are in complete rebellion against Him. However, the very act of torturing the damned is an act of rebellion on the part of the demons, because they were created to be good angels who love both God and humans; the role of tormentor was never something God wanted them to take on. It's simply the logical consequence of all the aforementioned circumstances which I laid out in this post.