We all sin, I agree. We are not all born in sin. If this was so, then to conceive a baby is sin. Sin entered the world, not the humans. Because we have a disposition towards sin, we all will sin, once we understand and violate our conscience. A baby is sin free, or else they would not inherit the kingdom of God. Original sin is not a biblical doctrine. All have sinned, yes, but that gets into the age of accountability.
Romans 5
12Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned13(For until the law sin was in the world, but sin is not imputed when there is no law. 14Nevertheless death reigned from Adam to Moses, even over those who had not sinned according to the likeness of the transgression of Adam, who is a type of Him who was to come. 15But the free gift is not like the offense. For if by the one mans offense many died, much more the grace of God and the gift by the grace of the one Man, Jesus Christ, abounded to many. 16And the gift is not like that which came through the one who sinned. For the judgment which came from one offense resulted in condemnation, but the free gift which came from many offenses resulted in justification. 17For if by the one mans offense death reigned through the one, much more those who receive abundance of grace and of the gift of righteousness will reign in life through the One, Jesus Christ.)
18Therefore, as through one mans offense judgment came to all men, resulting in condemnation, even so through one Mans righteous act the free gift came to all men, resulting in justification of life. 19For as by one mans disobedience many were made sinners, so also by one Mans obedience many will be made righteous.
20Moreover the law entered that the offense might abound. But where sin abounded, grace abounded much more, 21so that as sin reigned in death, even so grace might reign through righteousness to eternal life through Jesus Christ our Lord.
Romans 1
18For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, 19because what may be known of God is manifest in them, for God has shown it to them. 20For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse, 21because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened. 22Professing to be wise, they became fools, 23and changed the glory of the incorruptible God into an image made like corruptible manand birds and four-footed animals and creeping things.
Now how can they surpress truth if they never knew it? Unless one is born in truth.
Matthew 18
1At that time the disciples came to Jesus, saying, "Who then is greatest in the kingdom of heaven?"
2Then Jesus called a little child to Him, set him in the midst of them, 3and said, "Assuredly, I say to you, unless you are converted and become as little children, you will by no means enter the kingdom of heaven. 4Therefore whoever humbles himself as this little child is the greatest in the kingdom of heaven. 5Whoever receives one little child like this in My name receives Me.
6"Whoever causes one of these little ones who believe in Me to sin, it would be better for him if a millstone were hung around his neck, and he were drowned in the depth of the sea. 7Woe to the world because of offenses! For offenses must come, but woe to that man by whom the offense comes!
10"Take heed that you do not despise one of these little ones, for I say to you that in heaven their angels always see the face of My Father who is in heaven. 11For the Son of Man has come to save that which was lost.