I know many Catholics who don't find the Da Vinci Code offensive, because they understand the difference between fiction and non-fiction.
I too,know of many catholics who don't find the Da Vince Code offensive but it is because they bought into the prevailing zeitgeist and feel that their subjective,emotion based opinion,grounded in feeling not reality or truth or fact means something. It doesn't.But their inability to recognize that their opinion without a basis in facts,also makes them oblivious to whether a book is fiction or non-fiction. This is what makes them vulnerable and the targeted population for this type of tripe.
Surrounded by many others who also lack intellectual or spiritual depth,they create a danger,not so much to the Church,who Christ will accompany to the end,but to the survival of our nation as we know/knew it.
BTW,it is also quite obvious that some people who are very bright are among those that are cavalierly dismissing this as "just fiction,nothing to worry about",those are the real enemies of the Church but I do think The Da Vinci Code will boomerang and that is a somewhat informed opinion based on the reviews of the movie.