Don’t confuse sin with immorality. Sin is simply missing the mark of God’s Plan.
It wasn’t God’s Plan for Adam to have sinned in the Garden.
The sin is passed genetically from the male to each generation of human.
All humans has missed the mark of God’s Plan. None are qualified to provide an appropriate sacrifice for that which they denied God, our spiritual fellowship, because we are all spiritually flawed.
Only Christ Jesus, in His perfect humanity was qualified to perform that task.
The splitting of the veil in two and the Resurrection bear testimony to this success.
"Sin is simply missing the mark of God’s Plan." - Agreed. Notice that your definition indicates that sin is a verb: "missing the mark". You have to do something - physically or mentally - to sin.
"It wasn’t God’s Plan for Adam to have sinned in the Garden." - I think I agree with you here, and would add that God laid the foundation for forgiveness before he laid the foundation of the world (1Peter 1:20). So maybe a better way to say it would be that Adam and Eve's sin was not God's will, but he already had a plan in place before he created them.
"All humans has (sic) missed the mark of God’s Plan." - Those who have sinned - that is, acted against the will of God for man - have missed the mark. Per the passage I cited earlier, "sin is lawlessness."
"Only Christ Jesus, in His perfect humanity was qualified to [provide an appropriate sacrifice]." - Agreed. But if by this you imply that humans are not created perfect by God, then you have God creating dead spirits. Adam and Eve were created perfect by God and I would hope everyone would agree that God does not create dead spirits. If so, then we all have a perfect human at some point until the spirit dies due to sin. The only question is how this happens. Your position is that...
"The sin is passed genetically from the male to each generation of human." - I notice you cite no scripture. My position - and scripture's - is that "the soul who sins shall die." (Ezekiel 18:4, Romans 6:23). (Just like Adam and Eve, by the way.) Quite frankly, to imagine that sinfulness is a physical genetic problem is ridiculous in light of scripture, which teaches that sin is a spiritual problem, and redemption is a spiritual cure. As Jesus taught, "he that believeth in me, though he were dead, yet shall he live" (John 11:25)
Finally, to repeat a previous citation, "death spread to all men, because all sinned." (Rom 5:12) Not "because all inherited sinfulness from their father."