Romans 3:23 - "for all have sinned and fall short of the glory of God..."
My sin may not be particularly great or grievous compared to other human beings. I know that the fact that the world is tainted by even the smallest sin is a great and grievous matter in God's eyes. Theologically, it makes sense. Psychologically, expressing it this way may have some of the drawbacks identified in this thread.
I've just returned from the (Catholic) National Safeguarding Conference where, to my surprise, we used the 'I Confess' at Mass every day, and there seemed to be no problem with congregation saying it from memory (Mass cards/sheets/books etc. weren't available unless you brought your own.) On the subject of striking the breast it seemed that most did, three times.
In the parish I use all of the alternative PAs regularly, but I'm opting for the 2nd form slightly more often, to try to ensure we learn it whilst we have the text in hand (as it wasn't known in our parish before the change to the new translation).