Everyone one is conceived "in iniquity". Who says so? David:
Psalm 51:5 New American Standard Bible (NASB)
Behold, I was brought forth in iniquity,
And in sin my mother conceived me.
What is iniquity?
As a result of the fall men are born "bent-to-self". The modern phrase for that is men are born knowing only selfishness and self-love. This is not an act, but a condition. Because I was born with self-love I think selfishly.
Because as an infant I thought selfishly I naturally was selfish. Everything thing we do from birth is based on self-interest and self-love. That makes us sinners.