Why is it not just? They have committed serious sins, so they must be punished. Seems to me like letting them go for nothing would be the real unjust option.
What does “life of mostly good” mean?
Why do you seem that all these people will go to Hell?
Yes. This is why eating from the tree of knowledge was a bad thing.
There are two men in a village. Neither know God or what is a mortal sin. One man leaves to seek to know God so he can live in his ways. The other says, “I will stay here, I am happy as I am.”
Also, do you not believe that the more you know God and the more holy your life becomes, the more you experience the joy of his kingdom on earth?
what in your opinion would a just God do? what is your definition of justice? the actual definition is rendering God his due, namely obedience and worship. Sin of course is the obstinant deliberate refusal to do this. Recall that mortal sin requires full knowledge as well as grave matter and full free will consent. There are many whose education is so faulty that they do not understand these sins as grave matter or offenses so their guilt would be mitigated or altogether lacking.
Then you might as well complain about pretty much every legal system to ever exist. A person can live a “mostly good” life (however you define that), but if they murder somebody they will be put in prison. Even if they are someone who has done an enormous amount of good, for that murder they will still be put in prison. An easy way to imagine this, is to think if Mother Teresa (let’s pretend she’s still alive) killed someone, for whatever reason. Yes, a strange thought, but bear with me. Wouldn’t a just government be obliged to put her in jail, instead of letting her off the hook? The same goes with punishment for sin. If God did not dispense justice the way he does, he would not be a good God.
Ah, but to live the fullest life possible you should try and learn about God. Which also entails learning about things that offend God.