"G-d said, 'Let us make man.'" All of creation is done by G-d alone. Only in creation of man does G-d say "Let us make man."
G-d created animals and He created angels. Both are created in a state of completion. Now, G-d wanted a different type of being, one that is created essentially as an animal, but which, by his own efforts, will subdue his animalistic drives and become spiritual. G-d could have created man fully spiritual, but then he would have been an angel, not man.
Our character defects are part of our animal being. We have the ability to be different than animals, eliminate the character defects, and become what G-d intended us to be, not an angel, but a spiritual human being.