Real harm can be done from having an unresolved, interpersonal conflict being made public, because next step in Matthew 18 is banishment- making a church member an outsider. I have known individuals who have been deeply wounded by such a process. I still consider these folks fellow believers, even though they may have decided to avoid churches altogether.
The issue of “binding” is to first do no harm. The restraint of evil is what God is already doing, and it is a significant, if forgotten, ministry of the church, even as I let “loose” the good in ministry to he world. Great harm or great good can be done depending on how honest disagreements are addressed.
The body of Christ is like a human body, so think in terms of a human organism. Being a member of the body of Christ, I affect the rest of the body. The health or disease of the organism, the church, makes its own witness to the love of God in Jesus Christ. More than that, we pray to be “one with each other,” at Christ’s Table, Holy Communion.
What if the harm happened long ago, or the person involved is no longer alive but still in my memory? It’s still possible to make peace. In the Lord’s prayer, I pray God’s forgiveness and peace for others, and also ask for God’s forgiveness and peace: “Forgive us our trespasses as we forgive those who trespass against us.” If the person is far away, or if it’s unwise to go to them, I can still make amends by doing good for a person who is currently apart of my life. I can make peace by “paying it forward.”