Yeah, all the Halloween crap has always offended me, a Christian, yet the ghosts, witches, and goblins still hang from every classroom door in October. This person does not have the right to go through life unoffended.
Depending on how much time you have to devote to this, you can do quick things like phone calls, maybe even calls to your local news outlets, or you can give it much MORE of your time and energy by committing to a prolonged fight. It’s amazing what negative public pressure can do to these wimpy schools.
IMO, the government-run schools are hopeless and have been for a long time. However, even if you decide to withdraw your child and put him in home or private school, I would not go down without publicizing this to the hilt. At least make this experience worth SOMETHING.