Those people who are amazed at how happy some seem to be at the thought of all not being saved are essentially spoiled children who have not truly known injustice.
I don't think that's fair.
Not everyone will be saved, I know that. But I don't feel particularly happy about it.
Salvation isn't about what a person has done.
I dare say there are some murderers/rapists who people hope will rot in hell, yet they may have become Christians in prison -showing true repentance, not superficial in the hope of early release. I read about someone, years ago, who became a Christian on death row, but accepted he had to pay the penalty for his crime.
Some people who are, or have been, criminals, cruel dictators or committed vile deeds may still repent, or have repented. King Ahab was a weak, cruel OT king, yet he turned to God.
We may be unhappy at the thought of them being saved but the Lord can still save them.
On the other hand, some people who live good lives will not be saved because they refuse to believe in, or accept, Jesus.