I personally do not find the Confederate flag offensive, but it's not a good idea to fly one imho because of the continued slicing and sectionalizing of American culture. We have Hispanic-Americans, African-Americans, Albanian-Americans, etc, etc, ad-nauseum.
Match that with the heartfelt need by some in those groups to remind others of their "roots" or "heritage" by prominant display of flags of their ancestery and you really wonder who the "Americans" are nowadays.
The Confederate flag simply plays into that mentality without meaning to imo.