What is the effect of saying that Christ is not God?

Mala Chindongo explains in this video that there are still abuses that occur in the church with regard to the deity of Christ. These involve many heresies. 

For instance, when you say that Christ is not God, then He is a mere man who couldn't forgive sin. It maligns His work on the cross. 

John 1:1-3 (NKJV) - "In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made."