If someone is in such a state of open rebellion to God, then Paul and Peter tell us to examine ourselves to see if we are in the faith.
I'm not sure what that means as a response to the question: "...if we do not confess - He would not forgive us our sins and cleanse us from all unrighteousness?"
I guess I am looking at this from a position of humility vs. arrogance. Meaning if we do not confess our transgressions against God, then we are lacking humility. As John says he who says he does not sin is a liar. In our language that could mean denial.
I am of the mind to examine in prayer every morning, throughout the day and at night how I have served my King. Then to ensure I examine His Word for guidance and growth. For me this is analogous to thoroughly washing oneself in pure water (His Word and example) each day. As we say in the military this keeps the lines of communication open at both ends.