Why all the fuss about The Da Vinci Code, since it's just fiction?
The short answer
The Church as an institution has made no official statement on the book. The concern comes from faithful Catholics who saw it confuse people about the early Church, Jesus and Mary Magdalene, and Christian doctrine — and Dan Brown himself presented it as based on fact. Calling a work fiction does not license spreading historical falsehoods.
No official verdict
The Church has not commented officially on The Da Vinci Code, placed it on any list, or imposed sanctions.
Who is concerned, and why
The concern comes from faithful Catholics, clergy and lay, who have seen the book confuse Catholics and other Christians about people in the early Church, about Jesus and Mary Magdalene, and about orthodox Christian doctrine.
"It's only fiction"?
Brown himself promoted the book as the fruit of factual research, opening it with a "Fact" page. He wants readers to believe his conclusions. And even without that, fiction gives no right to spread historical untruths. A novel claiming the Holocaust never happened would rightly be rejected as propaganda, not excused as "only a novel." The same reasoning applies to other books that spread historical falsehoods.