I suppose God can do anything He wants but how is this "just"?
For the same reason that I can be justified in doing whatever I want to a cup/jar I've just made, a computer program, or a sentient AI. God could have created us and damned us to hell, went on a rampage and laughed at all the miserable people praying to him and slaughtered them just for fun. Hey, I've played
Black and White and I used to have fun tossing my villagers around, burning them up with a miracle of fire, throwing them a mile away, and laughing when my pet unexpectantly ate them. I was also usually helpful to my people in that game. I did quit the game, though, and threw it in the trash later because I didn't believe that making oneself God was an appropriate lifestyle.
I don't know how to reconcile the concept of eternal damnation with our own consciences, but throughout all of history those who have followed God have been used of God in ways that would teach us a lesson such as Job or even Solomon (and their lives - as far as I know - have been meaningful in the least; greatly rewarding - such as Solomon's early life). Job followed God and Satan wanted to see if Job's character was in err. So God said something to the effect of, "Alright, go ahead and see for yourself, but I know that he will not reject me." God allowed Satan to kill off his family, allowed his wife to tempt him, allowed him to inflict Job with boils, etc. etc. All his wealth and loved ones were lost in a moment. However, since Job remained faithful to God, God gave him more children and greater wealth (as I remember). Satan was proven false again and this time he could see for himself that this one man - this wretched human did appear to have greater character than himself.
Job's children who were killed in this trial, I believe, would still be fine off if they were as Job and had not rejected God. I'm sure if they remained faithful to him, their deaths would be transient and they would be filled with life again just as the Faithful and Believing will be. In essence, their lives were used for a purpose and if they had been faithful to God, they will live once again. There is a passage in scripture (Romans 4:3/Genesis 15:6) which gives me the impression that we are made right to God by our faith. Is faith illogical? I really don't think so.
In Genesis we have God speaking the universe into existence. How can God speak the universe into existence? Did he use Hebrew, Greek, English, Latin, or some verbal variant to utter the sun and stars into existence? I, personally, don't think so. I think he used a universal language that we could all understand - with his words being the stars and the planets. Genesis, in my opinion, is very metaphorical as I believe Revelation is. And even some of these metaphorical passages are explained within their context. Christ spoke in parables and explained them later. Like Father, like Son, right? ;-) But if the worlds and stars are God's words, telling us that he exists and that he did create the universe, then wouldn't we be calling him a liar if we did not have faith in him? Or rather what atheists prefer - a lie.
No, they failed to believe in a deity who cannot be seen and who's existence cannot be proven
My existence cannot be proven for certain either. You cannot see my face, but you can see my words. So while it cannot be proven that I exist for certain, it can be assumed that it is likely probable.
Sorry to get off on a tangent there. To summarize my point on hell - it may be metaphorical; it may not be. If it is not, God can do whatever he wants with his creation and it would be his right - though it might not appear to be very merciful. But then again, using a Scapegoat to inflict the injustice of the sins of the own people upon so that the sinful people can be transformed and enter paradise is not our idealistic version of justice either. This falls under the concept of "The good of the many outweighing the good of the few or of the one". Many of us, though, would probably say that a child is worth more than ten murderers. To those who have done wrong, they should suffer for that wrong. Eternally? It depends on if they wish to spend eternity with God or reject him and all that the rejection entails.
Well, there're my thoughts on the subject. I have faith that there is a reasonable explanation, but I do not sit idle and hope that I suddenly have a revelation. I search for it. Any reality where one's eternal self is in question deserves an answer - no matter your beliefs.