Cast not the first stone!!!~
Or were you trying to say that we are not to discern good from evil???
Hebrews 5:13-14 Anyone who lives on milk, being still an infant, is not acquainted with the teaching about righteousness. But solid food is for the mature, who by constant use have trained themselves to distinguish good from evil.
Based on this Scripture we are to discern (distinguish) good from evil. Even in the portion of Scripture you are referencing...John 8:1-11...there is discernment of good verses evil. The point was that God is the only one who is not guilty of sin and as such is the only one in the position to condemn the lady...to stone her...and He also had the right to forgive her. He did forgive her but then finished by saying “Go now and leave your life of sin.” So the original discernment that she had sinned was correct.
Romans 3:23 For all have sinned and fall short of the glory of God.
Romans 6:12 Therefore do not let sin reign in your mortal body so that you obey its evil desires.
So what is sin? We have all done it...so let's study His Word so we can discern good from evil.