Back to the original question however, the magnitude of ones sin is also weighed by the circumstances.
1. Do we know it is a sin and offends God?
2. Do we will to offend God by doing it?
Some things are innate, murder, robbery, unprovoked assault, these things if we are not impaired are things we always know are wrong.
Throughout the history of the Church there have been people who have not been taught their obligations to God. To worship Him is an obligation, but if someone is not taught that it is God’s Law and a Precept of the Church to Worship Him on Sundays and Holy Days of Obligation, one is not held culpable.
As another example, when I became a Catholic I was told by a priest that fleshmeats on Fridays during Lent where not permitted. I asked what fleshmeats where, he answered, “warmblooded animals” I asked the butcher if chickens where warm blooded or cold blooded, he told me cold blooded. That first Lent I ate Chicken or fish on fridays, someone who knew I had become Catholic told me I could not eat chicken, I asked the priest again, and he told me nope, no chicken, but as I had been ignorant of the law, I was not guilty of transgressing it.