Given that sin is not a debt - it's a crime against God - why do some say God only had to forgive? What about justice? Is God not just?

This is somewhat similar to this question, https://christianity.stackexchange.com/questions/82971/are-there-christian-denominations-or-movements-who-believe-that-jesus-didnt-act but **I wish to pursue the matter of God being the Righteous Judge of all the Earth** (Genesis 18:25). People are forever saying we have ***"a debt of sin" that Jesus "paid for", but I wonder if such language is clouding the issues here?*** Would it be right for any Judge to wave a hand and say, "Yes you are guilty of all those crimes but I'm just going to provide you with a free pardon. I expect you to be so grateful, you will then be a reformed character who will start to do good instead of doing evil" ? However, if the one sinned against arranged with his guiltless Son to bear all the punishment for your crimes against God, so that justice would be served that way, then would not mercy and justice have kissed at the cross? Does this not make sense of Romans 6:23, that we receive our well-earned wages for our sin - death - and after death comes divine judgment (Hebrews 9:26-27 & Revelation 20:11-15) which determines our eternal state? Then those for whom Christ bore the punishment for their sins are freely pardoned while it still remains to be endured by those who had no faith in that provision, effectively rejecting it? ***I would appreciate answers from those who claim there's no debt; God has but to freely pardon believing sinners.*** How can that square with perfect justice ordained by the Holy and Righteous God? Can we really expect no punishment in any form for crimes against God? Given that nobody from the group I addressed the Q to has answered, and 12 days have passed with nothing happening, I will now open the Q to those who believe in the grace of God to undeserving sinners, but to seek their ***views on how God's mercy does not over-rule or undermine his perfect justice. It's not the grace and mercy of God that is the question, but how that 'fits in' perfectly with God being the Righteous Judge of all the earth, as per Genesis 18:25.***