>In some Christian groups, everybody has to claim "I am a sinner"
That is the entire basis of Christianity.
A real Christian understands this.
The basis of Christianity is that we need a Savior, a Messiah, because we are incapable of saving ourselves.
Someone who isn't a sinner, doesn't need to be saved.
No matter how good a person might seem to be, there is no person who is perfect. Only God is perfect.
Therefore, God humbled Himself, because He loves us, and took on the form of a Human and sacrificed Himself for our sins.