What's the problem? If they make shooting optional, they'll have to make all the activities optional, which a) would be a night mare to administer, and b) is not the point of a school trip.
Everyone has to do things they don't like sometimes, if they are doing something as part of a group. You can't please all of the people all of the time.
What exactly is your point? Do you want to be able to opt DS out (and if so, why), or what??