I absolutely agree. But He never mentioned the need for a single sin free human to bring Him into the world. And He did a pretty complete job of explaining the rest of the process. I can find no Biblical support for the existance of any human after Adam and Eve that existed without sin. In fact, time and again the Bible explains that we ALL have sinned and fall short of the glory of God.
The only way I can understand how Catholics understand Mary is to study Catholic doctrine and the teachings of Catholic Church fathers. With that in mind, maybe you can understand why non-Catholics find Catholic Marian devotion so confusing.
No doubt it is confusing. I am confused by some of the things I think Protestants are taught as well. With study, prayer, patience, and kindness, perhaps we will all learn from each other.