Just because something is controversial doesn't mean it should be avoided because it offends people.  Exposure to controversy will still continue to happen outside of the classroom whether people like it or not.  It's all about preparing students for the future.  Teachers are already overworked with large class sizes and stringent testing policies, and students cannot be coddled throughout their education into thinking that a "safe" viewpoint is the only viewpoint that exists.  Although all parents may not like everything taught these days, a little bit of discomfort pushes us all to the realm of learning new ideas and understanding new viewpoints.  To ignore controversy in favor of myopic views on life will only lead to trouble down the road on personal, local, state, and global levels.