Christian views on what original sin actually is and its impact can vary.  The Catechism has a very good presentation of the Catholic view and is well worth the read (paragraphs 396-421).  Here is a summary:

• We cannot understand evil and misery in the world apart from our connection to Adam’s sin.
• This sin has been transmitted to us by Adam and this is a mystery we cannot fully understand
• Adam received original justice and holiness not for himself alone, but for all of human nature
• Adam and Eve committed a personal sin, but this sin affected the human nature that they would then transmit in a fallen state
• For their descendants, original sin is a sin that is “contracted” and not committed. It is a “state” and not an “act”
• Original sin is not a “personal fault” in Adam’s descendants
• Human nature has not been totally corrupted. It is wounded and inclined to sin (concupiscence) and cannot be conquered without God’s grace
• Baptism, by imparting the life of Christ’s grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.

The Catholic doctrine of original sin was more fully developed by St. Augustine in fighting the heresy of Pelagianism.  Pelagius taught that a person could lead a morally good life by the natural power of free will and without the necessary help of God’s grace.  In Pelagianism, the influence of Adam’s sin is reduced to a bad example rather than a wounding of the nature he has passed on to his descendants.  St. Augustine’s stance and that of the Church is that only God’s grace can heal this wound and transform us into the image of Christ.  We cannot heal ourselves.

As a consequence of original sin, we all suffer from what the Church calls “disorders.”  People often bristle at that term and can tend to be personally insulted by the implication.  I’m not sure why people take it personally.  As I said, we all have them, albeit often very different ones from our neighbor.  One tendency we can have is to recognize those in our neighbor while failing to see the ones within ourselves.  Or if we do recognize the ones within ourselves, we can tend to minimize those particular disorders as not being “that bad,” especially when compared to those of another.  Perhaps that is why we can feel insulted when our particular disorder is named as such.

These disorders can take many forms – physical, emotional, psychological, sexual, mental, intellectual, moral.  Many disorders do not have a moral component, such as a physical defect of some sort.  Others have a moral component because they lead us to desire acts that are objectively sinful.  An example of that could be alcoholism.  It is widely recognized today that a person can have a genetic predisposition for an addiction to alcohol.  That disorder in their nature can lead them to the desire to over indulge in alcohol to the point of drunkenness, which is objectively sinful.

It’s important to understand that the Catholic Church does not view having a particular disorder as being sinful.  Nor would we conclude that because we may be born with a specific disorder that means that “God made us that way.”  It’s part of our fallen nature, and as I said, we all have disorders to deal with, and our specific crosses to carry.  So there is no sin in having a genetic predisposition for an addiction to alcohol.  None whatsoever.  The Church does teach that to yield to that desire and become drunk is an objectively sinful act.  You can apply that same reasoning to basically any inherent disordered desire that attracts us to a specific sinful act.  The Church does not discriminate in this regard.

What do we mean by “objectively” sinful?  Simply stated, the action on its own merits is contrary to God’s law.  It’s harmful to both ourselves and the larger community.  It’s a failure to act in charity.

What the Church also teaches is that how responsible a person is for that action can be known only to God.  We can judge that the action itself is sinful based on the standards and teachings God has given us.  We cannot judge the person.

Consider for example someone who is gravely mentally ill to the point of being psychotic.  This is a disorder of their nature.  They may do many things that are objectively sinful, to include causing grave harm to themselves or others.  How accountable they are for their actions only God can judge.  Only He knows whether they made a deliberate choice to do harm, or if their reason was so impaired by their illness they are without personal fault.

One of the complaints I have heard from non-Christians is that the whole idea of an original sin of two people that has that kind of impact on all of humanity is grossly “unfair.”  The idea that we come into a fallen world with a wounded human nature through no fault of our own seems to somehow be a mark against the goodness of God.  This connectedness to each other and our world is indeed a mystery.

I think the entire experience the world has had with the corona virus highlights this connectedness for us in a profound way and can be an analogy to original sin.  Regardless of how the whole thing started, think of how the actions of a single person have rippled through the world at a rapid speed, and the destruction that has been caused.  Sin itself is very much like a virus.  As Fr.  George Florovsky (an Orthodox priest) puts it, “For sin does not belong to human nature, but is a parasitic and abnormal growth.”

Regardless of whether we think it’s “fair” or not, creation was designed in such a way as to have complete order and harmony.  When that order was disrupted by sin, a chain reaction occurred and continues to occur that wreaks havoc across human history and in our own lives.

The “good news” of this story is that as St. Paul says in 1 Corinthians 15:21-22 “For as by a man came death, by a man has come also the resurrection of the dead.  For as in Adam all die, so also in Christ shall all be made alive.”  And in Romans 5:18-19 he says “Then as one man’s trespass led to condemnation for all men, so one man’s act of righteousness leads to acquittal and life for all men.  For as by one man’s disobedience many were made sinners, so by one man’s obedience many will be made righteous.” 

So perhaps the “fairness” is found in that in one man, Christ, all things can also indeed be healed and made new.

Learning to recognize our own disorders and accept the call to do spiritual battle is an important part of our Christian journey to wholeness and holiness.  I find these words of St. Catherine of Sienna to be inspiring:

“I do not want you to fall into weariness or confusion through any vexations that you might feel in your mind; but I want you to keep that good and holy and true faithful will which I know that God in His mercy has given you … Yes, I want that out of the shadows should issue knowledge of yourself, free from confusion…Reflect that through love He keeps your will good, and does not let it run by its own consent or pleasure after the suggestions of the devil.  And so, through love, He has permitted to you and me and His other servants, the many vexations and deceits of the devil and fellow-creatures and our own flesh, solely in order that we might rise from negligence, and reach perfect zeal, true humility and most ardent charity: humility which comes from knowledge of self, and charity which comes from knowledge of the goodness of God.  There is the soul inspired and consumed by love.”