Through Christ, we receive mercy and avoid a fair judgement, the results of which not one of us truly desires. Those who sin without knowledge of Christ will ONLY receive a just punishment, the fact that Christians receive mercy and grace is not inherently relevant to the issue of justice for the unbeliever. No one will be found guilty who is not guilty, God shall be fair to the unbeliever.
Since salvation is the avoidance of just punishment, and is available to all who place their faith in Christ, the importance of Evangelism springs up. If those who were un-knowing of the Gospel of Christ were automatically forgiven, then Evangelism would in fact COST people their salvation. This seems to be the opposite of Biblical teaching.
"Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for all have sinned."
Romans 5:12
Absolutely wrong. Were either you or I present in the Garden of Eden? Did either one of us partake of the forbidden fruit? Of course not. But why are we under the punishment of what Adam did?
We are all guilty of evil. Each and everyone of us. Psalms 51:5 tells us, "Behold, I was shapen in iniquity; and in sin did my mother conceive me." Thus, we are guilty and condemned from the womb, without the knowledge of right and wrong.
And, while it is true that we deserve justice, it is better for us not to receive justice. Calling for justice and justice alone places all of humanity into hell.