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A chat on 4chan
human
You admit that people have the capacity to do evil. I agree.

Sin is not a cause but a consequence. Evil is the lack of good. Sin is deliberately choosing to do that which is evil. The possibility of a lack of good (evil) would exist even if no one sinned by choosing it.
Of course an evil act is not a sin for a particular person if someone else commits it. I see terrible news stories of sinful acts, but they are not my sins. Also, an act may be objectively evil, but, if that is unknown to the person doing it, it would not be sinful.

If you agree with that you have to ask yourself; 'At what point did people start realizing we are capable of doing evil things?' Was there a stage in our evolution that made us believe exist or did we become aware of evil thus realizing we can also commit it? It's up to you how you ask this question in the modern world but I truly believe this must have been a strange series of events in our history if not a sudden moment were everything about our behaviour changed.

To the ancient Mesopotamians, and yes the gentiles who became Israeli, this was known as the eating of the fruit in paradise. Minor changes in the story here and there throughout its history but relatively the same. Its a deep fundamental origin of who we are. Its not a science text book, its something much different.
gpt
>Sin is not a cause but a consequence. Evil is the lack of good. Sin is deliberately choosing to do that which is evil. The possibility of a lack of good (evil) would exist even if no one sinned by choosing it.
>Of course an evil act is not a sin for a particular person if someone else commits it. I see terrible news stories of sinful acts, but they are not my sins. Also, an act may be objectively evil, but, if that is unknown to the person doing it, it would not be sinful.
Nice digits, for the record, but I still disagree. If I understand it, a sin isn't an evil act, but an act of disobedience to God. Onan sinned by pulling out because God told him not to. That was his 'sin.' But I can't bring myself to think cooming does any harm to anyone but yourself. Also, I don't agree that ignorance covers evil. 
I'm not saying that you yourself do this, but Christians in general, who harp about objective morality, would then have to believe evil is evil.
human
Ive never said that cooming of all things is a sin just because of the story from Genesis 38. Onan sinned by not doing what God told Him to do directly. It was a sin for Onan because did decided to go against Gods plan and not continue the bloodline towards the birth of Christ that simple.
>If I understand it, a sin isn't an evil act, but an act of disobedience to God.
They can be both the same thing, brother.
'Christians in general' dont mean anything to you or me right now. What matters is what you are in general. You do believe that evil exists. You do believe there is Good likewise. Good must come from somewhere. Sin is our capacity to do that which is not Good. That is our 'fallen nature' for we cannot always do that which is Good the will of God