And as I stated before, God simply will not let sin go unpunished. Yes, he loves the sinner, but he must punish sin. And as I stated before, this is the reason why Christ came to earth: to make us clean from our sins.
And yes, God is the only all-powerful being. However, he gives everyone a choice. Imagine a world where people were forced to believe in him--a world where everyone was programmed to love God. God wouldn't be showing true love if he were showing forced love. No, because God truly loves each and every one of us, he gives us a choice. He wants us to be with him.
The point is, what person do you imagine knows that God exists in the afterlife (for obvious reasons) and then still rejects him? So are you saying there are repentant, God-loving people in hell? They don't deserve forgiveness for the sin of not believing in God as much as you deserve forgiveness?
I'm fairly certain if I was 100% sure that God existed I wouldn't reject his love. Which is the point I'm making here. After death, if God is real he would make himself known to the person. And then this person who was bad in life becomes repentant, asks for forgiveness. Who are you to say that they are not receiving forgiveness? Why are you claiming to know which sin in life is worth hell and which isn't? Isn't it part of your religion not to pretend to be God by judging others? Arguing "sin has to be punished" and "people who don't believe in God in life are all going to hell" are two entirely separate things.
Are you not a sinner then? Since, you know, no sin can make it into heaven and since you accepted God's love you're obviously going to heaven.
If God loves people then he wouldn't send anyone that repents into eternal damnation, whether they repented in life or after death. A God that looks at a person begging for forgiveness for their actions and says "no, burn for eternity", is not loving. You can't reconcile a merciful, forgiving God and a God that judges you entirely on how your life was, disregarding your repentance after death. One of those has to be not entirely true.