It is not the justice of God we seek. That would be US paying for all our own sins. It is His mercy and grace that gives us FREELY His forgiveness based on the shed blood of Christ for our sins. The problem we Christians see is that you Muslims are rejecting the payment that God Himself provided for your sins. That being the case, you have to pay for all of them yourself for all eternity. There are no scales. If you have one sin---just one single sin---that you are not relying on Christ to have paid for, you will pay for it yourself for all eternity. None of your so-called "good deeds" or "good works" will ever cancel out one single sin.
So, Christians see Muslims as mislead into thinking that they will ever get to heaven by their own efforts. Paul, writing to the Christians at Ephesus, put it this way:
Ephesians 2:8 For by grace [=God's giving us freely that which we don't deserve] you have been saved [rescued, delivered from..hell] through faith [trusting in, relying upon Him], and that not of yourselves; it is the gift of God,
9. not of works, lest anyone should boast.
Writing to Titus, Paul said:
Titus 3:4. But when the kindness and the love of God our Savior toward man appeared [=another way of saying "grace"],
5. not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit,
6. whom He poured out on us abundantly through Jesus Christ our Savior,
7. that having been justified by His grace we should become heirs according to the hope of eternal life.