I agree with Dude - if he doesn't need to go (for child care) and there's not an activity there worth doing, I'd withdraw him.
We have pushed our kids to attend camps that had an activity they wanted to learn, but were balking for an 'environment' reason - e.g. a robotics camp DD wanted to back out of when she realized all the other campers were boys and the counselors as well. In that case we worked with the camp director to switch her to an activity and group she was more comfortable with - i.e. it had a couple of girls.
In your case, I don't see the upside. I would try again later maybe with a better-suited camp. Age 5 is still pretty young - his sensitivities may lessen as he gets older, making it easier to tolerate noisy, crowded situations.
Also, it's a real bummer trying to cajole, persuade, bribe your kids to attend an experience that is supposed to be fun. (Having flashbacks to last summer. )
