I believe in Original Sin. What the Bible declares about sin is borne out every day.
First of all, what the Bible calls "sin" is not what most people -- even most so called professing "Christians -- believe it to be. Sin is any deviation from 100% obedience to God.
God created all things, and so he is the rightful owner of all things. He told the first man, Adam, that he could eat from all of the trees of the Garden, except for one tree. He said that in the day that he ate from that tree he would surely die. And when Adam disobeyed, he died spiritually. That is, he came under the judgment of God, and lost his ability to choose to do good.
His whole entire nature, his will, his faculties, -- everything about him fell into sin, so that he could no longer choose that which is good, but could only choose evil, all the time. And his sinful nature was passed on to his descendants, so that all of us are born in bondage to sin. And the only way out is if God works a miracle, by his Spirit, and puts a "new heart" in us.
Now, all of the effects of sin are observed all the time in this world: from little "white lies" to senseless violence, adultery, murder, ---you name it--- that's all a part of our fallen nature. And God is not to blame! It's US who are guilty! Even if we don't commit certain sins in the world, we commit them all the time, in our thoughts, and in our "hearts," where no one except God can see them.
And so, even as through one man, ---that first man, Adam --- the world was condemned, even so, through Christ, who is called "the Second Adam," all those who were appointed by God to salvation must and shall be saved! Christ came to this world to pay the sin-debt in full for his chosen people -- not those who chose him--but those who were appointed by God to salvation, and given to Christ, before he made the world!
Christ lay down his life as an atonement for sin, shedding his own blood to pay the ransom price for the sins of his people. And God accepted him, and his sacrifice, on behalf of all those he came to save.
Now, if you don't believe that, it's because you have no spiritual life in you. No one will believe it, and rest their hopes upon it, and trust Jesus Christ, unless and until God opens their "eyes". The Bible declares that "the natural man" --- the man, in his fallen nature -- can not understand anything spiritual, nor does he desire to understand the truth, because it condemns him!
Most so-called professing "Christians" believe that they're going to heaven because they made a "choice" to believe on Christ and be saved. But the fact is, they could not have chosen Christ by their own will!
Their will is in bondage to sin, and only God can give sinners the faith to believe on Christ! So, those who have truly been saved understand and confess that their salvation is of the Lord! It's not in a decision that they made themselves, as an act of their own so-called "fee will", but it is the result of God's sovereign will being performed in them by God the Holy Spirit.