Actually, we are held accountable for those things we are "ignorant" of.
The words bolded are pulled from the same greek word παράπτωμα.
3900 paráptōma (from 3895 /parapíptō, see there) – properly, fall away after being close-beside, i.e. a lapse (deviation) from the truth; an error, "slip up"; wrong doing that can be (relatively) unconscious, "non-deliberate." HELPS Word-studies
Ephesians 2 clarifies we are responsible for ALL transgressions, known or not, against God. It teaches the fact that all sin makes us dead before God....not just the mortal sins. It's all sins.
Ephesians 2: 1-10
And you were dead in your trespasses and sins, 2in which you formerly walked according to the course of this world, according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience. 3Among them we too all formerly lived in the lusts of our flesh, indulging the desires of the flesh and of the mind, and were by nature children of wrath, even as the rest. 4But God, being rich in mercy, because of His great love with which He loved us, 5even when we were dead in our transgressions, made us alive together with Christ (by grace you have been saved), 6and raised us up with Him, and seated us with Him in the heavenly places in Christ Jesus, 7so that in the ages to come He might show the surpassing riches of His grace in kindness toward us in Christ Jesus. 8For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; 9not as a result of works, so that no one may boast. 10For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them.
As Jesus said, even as he was being tortured to death, "Father, forgive them, for they know not what they do."
This is a little out of context. The Jews knew who He was but the Roman soldiers did not understand the full ramifications of their actions. That Jesus forgave them for their actions indicates their guilt.
This indicates that there are sins which are "unto death," and sins which are "not unto death." The Church terms these moral sins (unto death, as in "a mortal wound" or "a mortal sickness") and venial sins (definition HERE)
A person might use the word sin to mean either (1) a grave wrong, or (2) a grave wrong + knowledge + consent. You've got to distinguish between one and the other. A gravely wrong thing always does objective harm, whether you knew it, or meant it, or not. It is always objectively wrong and objectively harmful. But it is not mortal TO YOU (subjectively) if you did not know it or did not intend it.
Consider if a mentally handicapped man with a mental age of two and a half years old, picked up a gun and shot somebody dead. It was still objectively gravely wrong, it was still objectively harmful. The dead guy is still dead. But the mentally handicapped person would not be subjectively guilty of first degree murder.
Or would you find him guilty?