12 Therefore, just as sin came into the world through one man [Adam], and death through sin, and so death [both physical and spiritual] spread to all men because all sinned—
It is important to note that the word “because” gives the cause for death spreading to all men. The phrase “because all sinned” refers to the voluntary transgression that Adam imputed to his entire posterity because he is the head of the human race. When Adam sinned, all of humanity sinned in him.
Physical and spiritual death are universal because man sinned in Adam.
God’s view is that all men sinned in the one sinful act of Adam. Adam was representative of all human beings (federal headship). Adam’s act was the act of the entire human race. It is important to remember that the point of this verse does not deal with individual or personal sins of people.
Human depravity is not the result but the cause of why we sin. We do not have to be taught to sin; we do it naturally. That is why we need a new capacity received from God to live a new life in Christ.