Because Adam sinned we are all born guilty. As the Westminster Shorter Catechism answers for question 17, Adam’s “fall brought mankind into an estate of sin and misery.” Every man didn’t eat the forbidden fruit but, because our representative did it, all mankind is guilty in him. “One trespass led to condemnation for all men” (Romans 5:18). “[B]y the one man’s disobedience the many were made sinners” (Romans 5:19). The sin of one became the sin of all. We bear the sin of someone else.
We also bear generational iniquities. The sins of our fathers are our sins, not in the same sense at the same time, but they are still sins we have learned, that we experience consequences from, and that we need to repent from. “Both we and our fathers have sinned; we have committed iniquity; we have done wickedness” (Psalms 106:6, see also Nehemiah 9:2; Lamentations 5:7). Likewise, we are part of a nation that will not submit to the Lord Jesus Christ. We experience judgment together; the IRS doesn’t appropriate less taxes according to personal righteousness. The Church, too, is the household of God. As part of the same household, the faithful kids don’t get to stay in their bedroom while the parents are evicted for refusing to pay the mortgage.
Daniel prayed for and confessed the sins of his nation in Daniel 9. Israel was in captivity due to the sins of the previous generation and the proper response was not to say, “It was all their fault.” The right response was corporate confession.
To you, O Lord, belongs righteousness, but to us open shame, as at this day, to the men of Judah, to the inhabitants of Jerusalem, and to all Israel, those who are near and those who are far away, in all the lands to which you have driven them, because of the treachery that they have committed against you. (Daniel 9:7)
What we do affects others. What they do affects us. We don’t confess the sins of groups we’re in so that we can distinguish ourselves from them but to associate ourselves with them. As you are connected to, or responsible for, others you are in it together.