Is hell empty ?

A friend sent me a resume of a presentation titled the afterlife: heaven, hell and purgatory. There Hans Urs Von Balthasar was mentioned. A quick googling informed me that he was famous (or infamous) for suggesting that Hell might be empty.  Dare We Hope That All Men Be Saved? he asked. Logically all loving, all saving Father would not left any soul left in Hell. This would hard to digest if we thought that all psychopath leaders like Hitler would eventually enjoy the same heaven as those who lost their life in Auschwitz tortured under his cruel command.

I guess the decision to send some souls to hell would be God's prerogative but faithful might ask about God's justice.  After all we would like to know how are we going to please Him as faithful. Random acting God would be hard to follow/obey as we would be clueless.

Some would argue that despite the romantic thinking of Balthasar hell is real and not empty even though despite Church declaring saints (confirmed to be in heaven) there is such thing as anti-saints (confirmed to be in hell)

I thought half of my heart would want God to be merciful that hell would be abolished but at the same time I believe we still need to have some guidance on the implication of being unjust to other human beings. If death is definitive and there is no alter life then the hope a just universe is empty as those evils human beings would escape the punishments as there is nothing left in the other side of death.

Of course all these would still be speculation. There is no way to empirically test any hypothesis. All we have is theology and I would suspect that theology is more or less affected by our understanding of ourselves, human beings. God that is completely outside our  experiences as human beings would be unthinkable.