The Apostle Paul speaks on the Biblical doctrine of Original Sin in the second half of Romans chapter 5, of which I've analyzed at http://www.bcbsr.com/books/rom5b.html But the Augustinian heresy of "Original Sin" is much different than the Biblical doctrine of "Original Sin".

For example, according to Augustine, "All sinned in Adam", which is a verse not found in scripture. It is a fabrication by Augustine. Augustine held that people are guilty not because they sinned but because Adam sinned, the guilt of sin being reckoned to the account of those who weren't even there at the time - that God prejudicially and unjustly reckoned guilt to the innocent, holding people accountable for things they had not control over.

Augustine, along with his theological offspring, might not use terms like "justice" and "innocence" in this manner - as one would normally think of such things, rather they think of God's judicial nature and the issue of guilt and innocence in much different terms than how they are normally used in the Bible and in society. In Augustinian theology God is just by definition not necessarily by his behavior. So God can reckon the innocent to be guilty and yet be considered "just" by those of an Augustinian theology - the term "just" losing its actual meaning. In actual fact Augustine portrays God as "unjust". For even the God of the Bible says, "Fathers shall not be put to death for their children, nor children put to death for their fathers; each is to die for his own sin." Deuteronomy 24:16 Perhaps Augustine made up a different god for Christians to follow.

Now along with the guilt of sin, Augustine proposes also a sinful nature was passed down. But while the Bible does speak of such a sinful nature, the Augustinian view of the sinful nature is much different than that of the Biblical view of the sinful nature. John Calvin - a disciple of Augustine - summarized the Augustinian view of the sinful nature with his term "Total Depravity". That is, people are so total depraved that they have no control over their behavior and can do nothing of themselves but sin.

So once again even when it comes to people's particular sins which they actually have committed, how can God justly hold people accountable for things they have no control over? Is the sin their fault? How can it be their fault if they have no control over their actions? Thus again the god of Augustine portrays himself as  unjust.

The doctrine of Total Depravity is contingent upon another Augustinian heresy - namely that of the denial of Free Will. Yet volition is advocated not only throughout the Bible, the church fathers much earlier than Augustine were very clear on the matter. See http://www.bcbsr.com/topics/cfathers.html#freewill

Such alleged "Christians" have seemingly entered the Christian community not through the door, but some other means. For they don't confess sin as it is. What is their confession of sin? That it's not their fault; that they have no control over their behavior; but that God reckons guilt to their account nonetheless.